Skimmer vs Main Drain

[doncaruana]

This seems like it's got to be dumb question, but I sure don't know the answer to it...

I have a valve on my suction side (I think I got that right) that switches between my (dual) main drain and my skimmer. Obviously the skimmer's function is self explanatory. But why wouldn't I want it all the way on the skimmer vs the main drain? Does the main drain facilitate better water flow/turn over? Maybe pull some of the colder water out of the deep part and replace it with warmer (when the heater is on).

Where do people normally leave these valves? All one or the other or just in between?

 

[JohnT]

Enough skimmer to clean the surface, but some drain to circulate better. If you close the drain and you get a bunch of leaves or debris in the pool and the skimmer gets clogged, you could burn up the pump.