On many aircraft the raised aileron will allow/cause the nose to raise (like the Classic Flash) and this adds drag. Different aircraft behave in different ways, some already have washout (tip TE higher than LE) and adding raised ailerons will reduce the lift severely (wing area/wing loading will affect how this affects!) Its a major thing to cover every possible affect/upside/downside.
Generally on models its done to add drag though.

Dw