different amp/cab options

hey guys. Lately I've been thinking about different ways to set stuff up. And I thought about in a live setting, it's really no different what you use because in the end it's all going through the huge mains anyway. So what's the difference between miking one speaker of a 4x12 cab and miking the one speaker of a tiny practice amp like a Fender champ or something? Say you had a champ and a Mesa Bottle Rocket distortion pedal (tube driven pedal that sounds EXACTLY like a recto just in a smaller package), you'd automatically have an excellent 2 channel amp with a beautiful clean and an awesome distortion channel. Add a few more effects before them and you'd have a perfect rig. So what's the incentive of buying a 3 channel monster like a hughes and Kettner Triamp or a Bogner Extacy with a 4x12 if you could get all you need out of something so tiny and affordable? Is there something a 4x12 has over something smaller even when it's miked? I say all this because on stage you have your keyboard/bass/other guitar player etc. complaining about your amp being too loud for the stage. The audience isn't hearing your amp anyway, they're listening to the mains. I'd rather hear what I sound like in the monitors anyway, so for those of you who have played huge shows, what do you think? Just thought I'd ask