Originally Posted by Andy_K

Yeah, the big-big problem with a too short chain is just too dangerous of a beast to mess with. I did it once...once! You're riding along, going up a hill, feeling like you need a lower gear, shift to a bigger cog without realizing you're in the big chainring, and WHAMMY! Your drive train just exploded -- chain into the spokes, probably cutting a few of them, bent hanger, and your derailleur has twisted itself into a pretzel. It doesn't even necessarily feel like you're forcing the shift -- it didn't for me -- the forces at work are just much more powerful than you'd imagine.