Probably depends on the pump. I would think with the 24 volt one you can leave it full open always. With a 120v chugger, it's likely unnecessary to leave the valve full open, tho with biab recirculation and that stainless basket, you're not going to run into compaction/vacuum issues.
I've had more cavitation issues when messing with a 3 vessel system rather than with a biab system. But the value after the pump is super convenient if you need to stop the flow quickly.
Here is how I set up my pump for cavitation issues, and to insert a temperature probe if I so choose. The highest "mini" value can be opened to let air escape or insert a thermometer probe with a special fitting.
Thanks for the reply sketchykg. I will be using the 24 volt Brau Supply pump and I decided to ditch the basket for a BIAB false bottom from brewhardware.com so it sounds like based on your response I can just leave both ball valves fully open.