When you live by yourself in a small place, sure, just reaching for switches seems perfectly fine.

In a larger household, with many occupants it starts becoming more useful.

Simple things like roll-backs on lights for spaces that haven't been occupied 'for a while'. Or sensing occupancy and adjusting lighting and other conditions (shades, HVAC, etc). Note "occupancy" not just "motion". The lack of motion does not necessarily translate to nobody being present (sedentary use of a computer, watching tv, sitting in a bath tub, etc). Simple schedules to 'clean up' unused lighting or devices. Like turning off car/bike/power tool chargers if they've been running 'long enough'. Or activating them with simple voice commands.

Do you 'need' any of this? No, of course not, but it does add a bit of convenience for not a lot of technical implementation/cost.