what you say is basically true..but the big difference is that the positioning of the speaker boxes at rehersal is usually never the same as on a live stage..at live performances the boxes all face outward..this cant always be reproduced at a rehersal space..so.. room size..equipment placement..and accoustics are always going to be different..
When you setup on stage, you're to..guitars are more often too much on stage rather than not enough..
Drummer PA. Cool idea.While I have seen talented sound guys deal effectively with too much stage volume, it makes his/her job a lot harder. For smaller gigs I find it's counter-productive to have too much power and too many speakers. Mic'ing instruments is silly in these cases because once you blow away the drummer's volume, the bottom falls out and the sound becomes a mess. My last band was flexible when it came to stage/PA mixes. We had a small powered mixer just for vocals and added things when needed. My amp (Carvin BX1200 and two DB cabs) had plenty of juice for all situations. Since the head was so flexible, I could dial up any sound I wanted in bi-amp mode but I always made sure not to blow away my drummer. My guitar player/singer ran his pedal board (Vox with tube pre-amp) into a 60W powered Tech21 speaker cab. If the room was bigger, he would add a second cab and angle them accordingly. My drummer was a big dude who didn't need PA help at small gigs. If the room was bigger but there was no house PA, we had a 6 channel little mixer with one or two powered 15" PA cabs just for him. Even with the help our amps and vocal pa could hang with him in volume no problem. So could our PA since we only ran vocals which don't require lots of power. I got the idea of adding a separate little drum PA from a local blues band who just blows me away. They sounded full and got everybody dancing, yet everything else remained clear and tight. The vocals were clean because there were no other instruments sucking juice out of the vocal PA. Bottom line is you don't have to spend a lot of money on a PA to get great results.
What do you mean the guitar player angled his multiple cabs?