If you're connected to "City Water" and pressurized, then turning the pump switch "On" would probably make little to no difference when flushing or even filling the toilet. However, typically the pump will come on or run for a short period while water runs in the toilet. You still wouldn't observe much difference in the toilet.
On the other hand we've been at a campground where the water pressure seemed a little low when taking a shower (for our preference). As someone suggested in a previous thread, we turned "On" the water pump while taking a shower and it boosted the pressure very nicely. I turned the pump "Off" for all other purposes in this situation.
Bob Bowers (Surprise, AZ)
2003 Alpine Coach 40' FDTS
2014 Jeep Cherokee Lattitude