So I was a bit confused by the pedal when I bought it but I kept using it. It can be a clean boost on the middle setting, and that is always useful.
Besides that though the two preamps are, well basically little solid state preamps. These have been used on records and live by famous people. That doesn't help you though unless you know how.
Basically - the RE and CE circuits have a certain EQ to them that can really work well with some amp/pickup combinations. Also the Clipping that happens at higher gain is very touch sensitive and stacks well with other pedals and adds light compression. So in a way this pedal is highly usable in any chain and dead simple to use with the two knobs. A Tone control imo was not necessary (you probably have tone controls on your guitar and like 5 other pedals, or 15 ;)).