I have a Samsung phone so I use their modes and routines.
I only really use 2 (4, really, since you need activators/deactivators). The first turns my wifi off when I leave the area around my house and on when I enter it, so I don't lose battery searching for wifi. The second turns extra dim on at night and off in the morning.
I use sleep mode and driving mode and that's really it. I haven't found any other uses for modes/routines that I really felt were necessary.
I wish I could set one to restart the phone every night but Samsung doesn't let you.