It depends a lot on how heavily you use your phones. I'm a heavy user and my batteries degrade heavily in 2-3 years. That leads to overheating, poor performance, and of course poor battery life.

The cost of replacing a battery is high for most phones. Sometimes higher than buying a new phone at a similar level of performance.

I'm doing 1-2 battery cycles per day. A light user might go through battery cycles at a quarter of my rate, and would not have those problems.