So many reasons.

Smart locks on doors that disarm house alarms when they're unlocked with a code. Lights that turn on when someone is in a room, and off when the room is empty. The garage door alerting you that it's still open around the time you go to bed. The house stereo turning itself off at a certain time on weeknights, and the house alarm system turning itself on at the same time. Being able to check that the gas fireplace is off after you've driven out of your neighborhood on your way somewhere. The house disabling the security system for 20 minutes when it detects you on the second floor landing, so that you don't trip the motion sensors when you go down for a snack.

A non-trivial example of some more complex things our house does: when one of our phones enters the neighborhood, and it is after dark, our carriage and porch lights come on. If no other phones are already home, some of the inside lights also turn on. When we turn onto our street, the garage door opens. After the garage door is closed, the outside lights turn off.

Any number of things ranging from small to large conveniences. Some small conveniences become large ones when you have guests staying over.

Edit: ooo, ooo, one other thing: I have a bunch of these switches around the house that have multiple buttons and are programmable (they recognize single click, double click, hold, etc). It allows me to hook almost any part of my house to any switch, without rewiring everything. I have several configured to turn off the alarm system, I can manually turn off all of the first-floor lights from the upstairs master, I have one in the entryway set to toggle a lamp in the office to avoid having to walk in there, navigate around the desk to the far side of the room, and switch it from there. I configured one to turn the gas fireplace on and off, because the builders had not seen fit to wire the controls to a wall-switch.