My reason for a wall of cabs is this. I want every single person in the crowd to feel intense vibrations, not just kick drum and a little bass like most heavy bands. This is about consuming people with sound ultimately leaving them zoned out and relaxed by the end of the set. Seeing as how many of the places we've played and will play have very little or no PA support and even if they did, wouldn't be willing to push their system as loud as desired, I'll be playing through a wall of cabs for a while.
Also, when you're in front of a wall of cabs at full volume, you're able to sustain notes and chords nearly infinitely due to the intense air movement going on near the rig, which considering how slow some of the music is I'm playing, is important to me. That type of feedback manipulation can't be done without a LOT of air movement behind you. I'm sure I could nail my tone with a smaller set up, no problem... but I could run a 1,000 watt amp through a 2x10 and it'd be nowhere near as loud or move the amount of air my rig (see sig) can.
Of course, there aren't too many genres out there with these goals in mind. Kind of a different set of wants and needs than more common types of heavy music that most are familiar with so take all this for what it's worth. I just say, use whatever works for you, plain and simple. If that's a 500 watt micro amp through a 2x10 or a wall of large amps and cabs. I don't see any of this as a "right or wrong" issue. Use what works for you and your band.