Just five years ago, 25c width tires would gather dust on bike shop shelves in favor of 23c tires, only to have the opposite happen a couple of years later. Fast-forward another few years, and 28c is now the go-to road tire size, but there are plenty of people going much wider, even for everyday tarmac-only riding.
Admittedly, a half tooth effective increase for your big ring isn’t worth worrying about, but when switching from road to gravel tires, the effect on gearing gets much more significant. For example:
28 to 45c = 2.03 tooth increase on a 46-tooth ring (effectively a 48.03-tooth ring)
28 to 45c = 1.46 tooth increase on a 33-tooth ring (effectively a 34.46-tooth ring)
28 to 40c = 1.50 tooth increase on a 46-tooth ring (effectively a 47.50-tooth ring)
28 to 40c = 1.07 tooth increase on a 33-tooth ring (effectively a 34.07-tooth ring)
However, when you consider switching from a slick 28c road tire to a knobby 40 or 45c gravel tire, not only do you get a significant increase in effective gearing, you also get a dramatic, easily noticeable increase in rolling resistance (including an additional small, but significant increase in aerodynamic drag). So, selecting lower gears for a bike with gravel tires makes a lot of sense when compared to a 28c slick on the same theoretical ride route.