This discussion is exemplary of why r.a.s is not a place to learn.
There is the usual low fact:fancy ratio and high fertilizer quotient, spiced with a little unwarranted personal vindictive.
The personal experience is useful, yet the only analytic comment that is sound is the quotation of Mark Maughmer. We need less "physics" and more aerodynamics to understand this phenomenon.
In addition to aileron drag, spanwise flow is importantly improved for ships without spoilers with a little slip (the proof of the pudding is in the eating). Regardless of improved climb, there's a real safety benefit: in a steep turn, in an un-spoilered ship with long wings, if the yaw string is kept centered, the stick will be hard against the top stop. Now there is only two-axis control. Thermal turbulence will readily cause an incipient spin, as I have experienced many times -- until I learned how and why to slip steep turns. Slipping the turn enough to (approximately) center the stick:
- most importantly improves control (a good thing for the spouse & kids, and the others sharing the thermal)
- decreases span-wise flow, improving the lift distribution, and
- decreases aileron drag, which probably improves turning sink rate, but more important, helps avoid stalling the inboard wing.
Ships with spoilers have improved circulation at the outboard part of the wing, decreasing the need to slip turns.
Credits: Dr. Mark Maughmer, Tilo Holinghaus