Chickens are not real long lived animals. It is not uncommon for some to die before 3 years of age. Also predators can wreck havoc. With small flocks of 4-6 birds, natural culling will often times be all you need. Feeding 1-2 non productive birds does not cost that much more.
When you start getting larger flocks of 12 +. then one must be more selective as who is in the flock and laying or brooding new chicks. The larger flocks, tend to produce more chicks, which tend to produce more roosters than can be successfully cared for in the set up. Culling become necessary for economic reasons, feeding a dozen birds that are not laying eggs, either roosters or old birds does cost money, the need for separate set ups for bachelor pens does cost money. Culling also become necessary for the flocks success. Too many roosters do not work well in a confined space of a backyard set up.
These are personal decisions, depending on your own set up, your own space, and your own emotional and economic realities. Most of us that do cull non- productive birds, have one or two birds that just get to stay because we like them.
Neither culling or non-culling is right or wrong for everyone, it depends on your place.
Mrs K