Flowrate ...high or low?

[|JTBC|]

I no expert but just wondering is it possible for the following reasons ?? :
Faster flowrate is good for mechanical filtration - to remove solid waste/unsightful particles;
Slower flowrate is better for bio-filtration - to provide adequate time for the BBs to do the jobs.
If so, the best of all is to have a system with control of flow for bio or mech filtration.