PROS:
You can hatch your own chicks, either to replace losses or if you want to sell some to offset your chicken-keeping costs.
Protection: How effective a rooster is depends on a lot of factors. A lot of people assume because some roosters get human-aggressive they're these little ninja-raptors that can drive off anything smaller than a bear.
The reality is even the meanest ones don't usually weigh more than 10 pounds, which barely puts them on even footing with a domestic cat, let alone something the size of a raccoon or the speed of a weasel. Plus, even most predators aren't really interested in an actual fight, and roosters are basically prey animals with the instincts to match.
That being said, I've seen mine drive off small predators more than once. Usually this is through bluster and posturing, although they did go after a hawk once (which resulted in two of them being injured).
More realistically, a good rooster keeps watch while the hens forage. Plus they tend to keep the girls herded up where they can watch them and keep an eye out for predators. I'd say most of the time what they do is spot trouble (well before I can even see the actual bird) and get everyone under cover and then get everyone to make a racket. Even the immature eagle that visited this winter didn't want to try his luck with the three dozen birds packed side by side under cover screaming abuse at him.
Keep in mind all these protective qualities only work in the daytime. At night they're just as blind and sluggish as the hens, and most predators will make short work of a sleepy rooster.
Third, a good rooster acts as a mediator. I currently have four, and the two lesser roosters in the pecking order will act as greeters to new birds I introduce, and will usually protect them from excessive bullying.
The two higher roos in the order, especially the alpha, will break up fights between the hens, and the alpha even stops fights between the beta roosters.
Finally, they're some of the most gorgeous livestock you can ever own: the fabulous plumage, the way the strut and pose.
CONS
First, they are NOISY. My copper maran makes my ears ring if he crows next to me. Sometime just before dawn they'll make a racket, and contrary to popular belief they'll crow all day long to show dominance, claim their territory, or if you have more than one they'll "sound off" to see where the rest of the flock is.
What people call the "egg laying song" is really an escort call hens often make before they lay an egg. Roosters often will repeat that call and it can make quite a racket.
Roosters also do this thing where they'll flirt by picking out a nesting site and calling a hen over: the nesting-call sounds more like some alien creature choking do death than any sound a bird should make. Creeped me out the first time I heard it.
If you've got neighbors near by, they'll complain. If somebody's bedroom is within 10 yards of the coop, they'll wake them up.
Second, roosters tend to be more "high-strung" than hens. Those same instincts that make them good protectors and flock leaders means they have some less appealing personality traits. A lot of aggressive rooster instincts are due to a failure to understand how their brains work and read the warning signs of impending aggression.
I also think roosters really need a spacious free-range environment to really thrive. Mine cover a lot of ground in a day, and they like to guide their hens to various foraging spots or sit down for a group dust-bath. If your backyard or run is measured in square feet instead of acres your rooster may start acting up just out of sheer pent up energy.
Second, if you're totally new to chickens or a hen growling or clucking at you seems intimidating, do not get a rooster. Many Roosters them will try to push boundaries with you, especially when they're younger or after the pecking order has shifted. It's something that if you ignore, or worse retreat from, will only escalate eventually into an attack.
Chicken-brains aren't wired for a relationship of equals, and there's a reason their social structure is called a "pecking order."
If you have little kids or one of those little yipping dogs, don't get a rooster. Things that dart around and make lots of noise will just hit a rooster's crazy button, and sooner or later they'll take a swipe at it. Most kids are incredibly stupid around farm animals, largely because most parents don't educate their kids properly: I know this from bitter experience: my first concussion was when I was at a montessori school that had a sort of petting-zoo-farm and nobody told me that a lamb staring at you intently is not an invitation to go pet him.
Third, If you tend to anthropomorphize animals (that is, interpret how they act is if they're people), you will be horrified at the mating habits of young cockerels. This is especially true if there's no adult roosters to keep them in check. They don't take "no" for an answer. Oddly it was two of the quieter adult legbar hens that started slapping some manners into my young "gentlemen."
Even when they learn to do it right, there may still be some feather loss to your beautiful hens. The only way for the rooster to mount a hen is for her to squat, and then he has to climb on top of her and grab the back of her neck with his beak to maintain his balance. Even if he tries to be as gentle as possible his favorite hens are going to get some feather damage as roosters are extremely randy.
Fourth, if you have more than 1 rooster, they WILL fight to establish the pecking order and any time something makes the pecking order shift. I had four shifts in my group between 9 and 13 months old, each time somebody got bloody (one of which was fatal).
Fifth, roosters in general are very prickly at social status. They tend not to like it if you toss treats to the hens, it's better to treat the rooster & let him call the hens to it. I have one that gets prickly over paying attention to him: most of them will come up & greet me if I show up in the back yard, but jackass is the only one that gets huffy if I ignore him.
The current alpha rooster does this thing where any time he sees me drop anything like a treat, he'll lead 4 to 8 hens over, chase the other bird or birds off that were there, and then make his tid-bitting call while his girls feast.
If you like petting and cuddling with your hens, I don't recommend getting a rooster. They don't have any real concept of what "petting" is, so any physical contact is related either to mating or fighting in their heads. If you're constantly picking up & touching your hens, his little brain might decide you're acting like a predator or a rival rooster and he'll start treating you accordingly.
In short: High-energy, high-maintenance, high-volume, but pretty and you can double your flock every month if you want to.