Originally Posted by dayhead
Perhaps you're familiar with the Swift hang glider design. The name stands for "Swept Wing with Inboard Flap for trim".
If your planform has enough sweep, you can lower the trailing edge in the inboard, or root area of the wing to get a nose-up pitching moment. In many cases this is better than increasing reflex in the outboard, or tip area of the wing. I use this to get better sink rates from my Sling Wings.
Isn't increasing twist better still? Increasing up elevator and deploying flaps both deform the airfoil. Increasing twist increases the difference of incidence between the root and the tips. Which is exactly the same as deploying flaps without making things draggy.
Flaps do have another effect that matters though. They can increase the camber of the root airfoil (or decrease if you deploy them "up"). This is what most RC glider pilots use flaps for - to control the behavior of the airfoil. This is neither better nor worse than increasing up elevator (indeed, deploying flaps often upsets trim and has to be accompanied by changes to the elevator). It's just a different thing to control.
For free flight stuff the same effect can be had by choosing different airfoils for root and wing tips.