I've toured for the past 8 years with an 18w Fender Super Champ, which has a 10" speaker. I generally run the master and channel volume on 6, but for smaller stages, it's way too loud and I have to drop the master back to 4 or 5. I keep it on top of its flight case, tucked in behind me. All of my gigs involve full production, and the guitar is always in the mix. FOH engineers love it. They don't have to wipe out all the frequencies under 120Hz that mush up a mix, and they don't have to deal with uncontrolled stage spill. Once you understand the logistics of what happens when the few milliivolts of signal delivered by the microphone reach the mixing console and run out through the PA's power amps and speakers, you realize that it is all about scale and tone. The only time it doesn't work is with very loud drummers in very small spaces. For that I'll use a 30w amp! It's not for everybody, but the results when you can make it work can be huge.
I use this rig...
For gigs like this...
Cheers................................... wahwah