As others said, fun and convenience.
For example: when I start a movie, the lights in my living room dim or turn off automatically. Sure, I could get up and do and set several lights manually, but I would probably not bother and watch a movie in a lit room. When I stop or pause the movie, lights go back to the normal setting.
If it’s dark when I get home and I open the front door, it starts the default lighting program. Sure I could fumble for the light switches in the dark, but it’s another convenience.