Hi, I've been a rhythm guitarist for short while now, and barley do any lead playing and I've heard that using a metronome will improve the tempo etc. but I've only seen people using metronomes for practicing single note lead parts. So, I wonder if using a metronome is also crucial for chord based riffs. Hope that's not too stupid of a question
The metronome will improve all of your playing no matter how good or bad you are. Use it every day, practice your chords/scales with it, practice different rhythms. You'll gain a lot of rhythmic precision.
A metronome is good for timing in all aspects of playing. Almost nobody uses a metronome enough (including myself). Even using it 5 minutes every day will be a big help.