pa or amp

i have a question, why would it really matter the power of your amp if it goes through the amp, i mean like why buy a full stack instead of a half stack, is that so you wont need to run it through the pa? I dont understand it that much because i wouldnt think that if you just played out of your amp and not the Pa you would not really get a good all around sound equally out of your guitar. So whats the purpose?

Not all places have monitors for everyone.A 4x12 pushes lots of air so you and others can hear you without cranking your amp to deaf rendering levels and distorting the mic(if your cab is miced).

Well this depends on whether you're recording or playing live. The cabinet colors the tone of your guitar a certain way, so if you use your amp's cab instead of going direct into the PA and using the PA's speakers, it will sound different. I've seen a lot of bands where they run their amps to a mixer then back to the guitar cab, just so they can keep that tone. Some just use the PA speakers though, if they sound good for a guitar. I know Sumbersed uses the house speakers, at least they did at the Electric Factory in Philadelphia. For recording, I'd say definetely run through your guitar cab, don't worry about volume, just crank it high and mic the amp. You'll get a much better sound than if you run it through a PA. The difference between half and full stack, it's pretty much two cabs will be twice as loud. Maybe not exactly like that, but it's much louder, so you can have that higher volume without running your actual amp as high. Sorry for rambling, I probably didn't need to say half of that, but I hope I helped.

but still, if you have a half stack you can mic it right and you could also run it through the PA if you wanted to, but do people get full stacks to just play directly to the audience from there amp because i wouldnt think that it would be good to do that becuase the sounhd would be coming from one side instead of out of the PA from both sides, im still confused

Well unless its an outdoor festival or something where you need to push lost of air,then a fullstack is not necessary.Your actually not even supposed to point your amp up front at the crowd directly...you want it to face the center of the stage or be angled outward from beside the drummer.

Even slayer with their walls of marshalls dont stick them up front,they flank the drummer at both sides.More speakers mean more sound/air pushed...thats it really.

You never put it right up front at the crowd. That's what my band does too, speakers on each side of the drummer, behind us. We can hear ourselves better that way too. What we do, is we have two speakers, one goes on each side of the drummer, and the amps go on the right, everything runs into the power amp and out to the speakers. Not a PA system, but our equivalent.