Okay so, the metronome's basic use is to give the beat of an intended tempo and to check rhythmic accuracy. I am split on wether a metronome is a helpful tool or just a mechanical device that ruins the 'groove' of the music. I have had teachers that strongly support the use of a metronome in order to create a strong sense of pulse and rhythm. However, I've also had teachers that focus on developing the human, or 'inner' metronome. I think both arguments are equally creditable.
Musicians obviously need to distinguish the correspondence between rhythm and pulse and need to be able to play accordingly. It is also a great tool for correcting complicated rhythm's and personally I've used it to stop me speeding up. On the other hand, Time is considered fluid, not robotic and metronome markings do not leave space for tempo to be altered within a song. Personally, I think it depends what genre of music is being played. For example, I would use a metronome to practice a rigid piano piece, probably renaissance Baroque and early classical. But for a romantic and emotional piece, tempo would possibly want to be 'pulled about' and therefore a metronome would be a hindrance rather than an advantage.
Within a group environment I think a metronome is extremely beneficial when a drummer or percussionist is not present. It keeps everyone at the same tempo, therefore creating a 'tight' sound. However, if a drummer is accessible I would prefer to use them. Even though they are probably not as precise as a metronome, they can keep the beat in an un-rigid way.
Overall, I think a metronome is a good tool for practicing solo. But I wouldn't recommend it for a group or for 'pulled about' songs.
