Now spoilerons, they're OK.

I have flaperons set-up on one model, but that one has tapered ailerons that don't extend to the wingtips. You'll note that in more advanced models with butterfly or CROW mix the outer ailerons lift (aka "spoilerons"). That gives added wash-out and prevents a low-speed stall. If you're slowed on approach and trigger flaperons you run a big risk of stalling one wing panel should you mistakenly try to correct a low altitude roll problem with ailerons instead of rudder.

Since 90% of flyers (not just beginners) would use ailerons in that situation, you can see why it's not generally a good idea. Flaperons down on slow approach near the ground, left wing drops, you give right aileron stick which lowers the flaperon on the left side even more and stalls the left wing completely. Model rolls left (opposite to stick input!), strikes a wingtip and cartwheels into pieces and you yell "I got hit!" instead of "I was dumb!"