I have parents and students asking me all the time, especially beginners, if they should be using a metronome. My answer is, always, yes, the student has to learn how to follow the metronome while the music is still simple. A lot of students are not expose to playing with metronome, therefore, when their piece becomes more complex, they have a hard time following. However, metronome should not be use to replace student’s feel for rhythm. For those who are beginners and early intermediate students who use the metronome all the time while practicing, you are running a risk of relying on metronome rather than developing a sense or a feel of rhythm internally. I have had transferred students relying on metronome so much, when you shut down the metronome, the students plays without a sense of pulse or rhythm completely!
For intermediate and advance students, because of the complexity of the pieces you are playing, one shouldn’t be using the metronome through out the piece. However, you should check tempi of all sections in the same piece of music to make sure that you are keeping the same tempo throughout the piece (unless there are tempo change indications by the composer, or to serve certain interpretation needs.)
Metronome is also a great tool for practicing. I have always use metronome when I try to perfect a certain section in music that is especially technically challenging. I start with a very slow tempo, usually slower than the tempo that I am already handling well, then increase one click every few times of repetition and slowly bring it up to tempo. This way, when your teacher ask you to practice slowly and increase the tempo slowly, you will know exactly what to do and to follow. I have tried this method over and over, and it never fails. You will learn how to play slow and fast and all the in between tempo of the same section, your fingers will develop great muscle memory, which will make your performance most secure even if you are too nervous to remember anything!!