It really depends on ones' situation. It is never a one size fits all.
If someone lives in the city and is only allowed 3 or 4 chickens, then no. Keeping a rooster there wouldn't be prudent.
If there are no prohibiting ordinances, one has more space and more hens then it is absolutely a good idea to have roosters.
At any one time, I may have between 40 and 100 chickens so it isn't unusual for me to have from 5-15 roosters.
If one is breeding and producing chicks, they don't want to get down to one rooster because if he gives himself up for the flock, you are out of business.
Add to that, if one is raising a specific breed, they should be striving for the best representatives of the breed. If that breeder only has a single rooster, they have nothing to compare him to except the SOP. However, if someone has 10 or 20 or 30 roosters, it is much simpler to improve the breed by selecting the best representatives for breeding purposes. It is then usually easy to identify candidates for culling.