The metronome is a great device for practicing new techniques and tunes at a variety of tempos.
The most effective way for using it is to combine it with the “Labyrinth” technique, which can greatly accelerate your progress.
Isolate out a particular section of a tune that you find challenging (can be as short as just a few notes) and start with the slowest metronome speed. Increase the speed as you become more proficient.