You would if you want to update... people who live for benchmarks, the shiniest and newest, etc.
I've typically done 2-3 generations (i.e. when Applecare runs out), but the pandemic really changed how I use tech. And these days I do have more of an inclination to run tech into the ground, especially as I have multiples of each thing which can also work as spares. I'm almost all-M4 now (except for an M2 Studio) and while I will be making some changes because I realized I under-bought, once everything is stabilized I'll probably stick with the setup for closer to 5 years now, so my next major upgrades will probably be for M9's, unless something drastically changes for hardware reqs.