People often say this but it isn't really backed up by the science. Sure, there's a bit more degradation, but not all that much. And by keeping it within 40-75 you're effectively limiting yourself to using just 35% of a perfectly healthy battery, giving you far less capacity than if you had just maximally used it. Even if after significant usage you end up with only 70% of the original capacity, that's still more than you get by artificially limiting yourself.
Extreme temps are a factor, but just don't put it in the fridge or leave it in a hot car and you'll likely be good.
See https://youtu.be/kLS5Cg_yNdM?t=183 for some actual testing on this.