Originally Posted by PseudoChef
I use two fermentors since I rarely pitch the same yeast for all 10 gallons.
To me, one of the most fun parts about making 10 gallon batches is creating subtle (or not so subtle) differences between the batches. I almost will use different yeasts, or different dry-hops, or add honey to one, or something like that. It's fun to see which one you like most (might surprise you) and is an easy thing to do to show other people how beer "works."
...that said, I'm in the middle of building one of the 15 gallon inductor tank fermentors!