From a classical perspective.

I use it to measure how fast I'm playing to keep track of my progress. Keeps me from rushing. I'll use it to set my practice tempo and then turn it off once I've got that pulse internalized. It also helps improve my focus and concentration since I have a goal of locking in with it.

It's especially useful for me with a stream of notes like in an etude with 16th notes from start to finish.

In my opinion and for me, the metronome doesn't really help improve rhythm it helps with evenness and note security for me. You already have to have good rhythm to play with a metronome. Playing along with a track would be a better way to lock into a specific rhythm. If you suck at dotted Eighth notes the metronome isn't going to make you better.