I would say that it is a fine-tuning of my tone, but absolutely essential. The difference shouldn't jump out at you when you play your instrument alone. In rehearsal or live setting, it should "magically" transform your sound from mud in the mix, to a tightly focused, easily discernable tone.
For me, it depends on the song. During loud, fast songs, I use it to keep the overall mix from getting sloppy. In slower songs with more "space", I keep it off, and then turn it on for leads.
Try to set your compressor so that your max volume is the same on or off. It can make you stand out without taking over the whole mix.