If the plane has flaps, and you don't run the ailerons on out, you
probably won't be able to use all or any of the negative flap for
higher speed running. The LS-3/17 manual says "Thou Shalt Not Use ANY
negative flap if you installest thy long tips." They didn't put
ailerons on their tips. The Nimbus 3 manual says "Thou shalt limit
the flap travel to -2 (block thy "S" position) if you increase the
span from 24.5 to 25.5 meters. Why? As Hank said, if you run the
flaps up and don't have aileron (interconnected with the flaps, of
course) on the extension, the tips pick up a LOT of load, as they are
at a much higher angle of attack than the rest of the wing.

If the plane does not have flaps, adding aileron will only complicate
your life.

The poly wing actually helps the plane "groove" a bit more in
thermals. It can also have the benefit of pushing the downwash field
down and outboard at the tips, potentially providing a small increase
in effective span. Or maybe, less of a decrease in effective span as
compared to a planar wing. And if your tip chord gets really small,
it makes it so you are less likely to drag three feet of wing on the
ground if a wing goes down on takeoff.

My nickels worth,

Steve