Here's how I think of it...
Hardware cloth can be expensive, which is one thing that puts people off about it...
but...
Monetarily, losing birds you have invested a lot of time and money in (think of the food you fed them to raise them, etc.) adds up if you keep losing the birds to predators, causing you to have to replace them. If you're planning on raising any types of rare birds or looking to start a breeding program, I can't imagine why you'd risk it.
Emotionally, losing an animal you really like, especially in the graphic way some predators destroy them, can be very taxing. If you have young children and the chickens are going to be their pets, it might be very traumatizing for them (not that I'm against kids learning "the facts of life"... it just seems right to protect a beloved pet).
Even if you lock your birds in the coop at night, hardware cloth is the "first line of defense" to anything that might be headed for your pop-hole door. It just makes it that much harder for predators to get in.