heh, go with the saying, if you aint sure whether you need it, most probably you dont.
take a deep breath, a step back and analyse, whether dynamics of playing style will affect the role of your playing in a band setting. Are you able to control the playing dynamics via picking hand or just wanna have a pedal that does it for you.
the sustain part of compressor which some might know, is actually quite a misnomer which prolly arise from boss having the "sustainer" word in their compressor.
At high setting, it doesnt literally give long sustain, but extreme case of compression which squashed the signal level, killing off the dynamics peak.
for some, the compressor is being used mildly for the compression and its tonal shaping ability on the overall chain of signal.
oh yeah, compression is used in music other than guitar. Its pretty common for recording, mastering purpose as well, but the funny thing is that only when use for guitar purpose, we tend to think of sustaining. Hehe, i blame it on boss.