Depending on the tank the output may be more than insignificant.
I have a 1400gph return pump for example. While I dont necessarily count it, I do consider it cause it actually does make my corals sway, even without a powerhead on.
I aim to have the most flow I can without fish struggling or sand blowing around. For me, it kinda works itself out in my head automatically lol. I have 2 1400's in my 90g fowlr
for instance with a return of 900gph. That is sufficent for that tank but gives me a good flow pattern. My 125g only has the wp40 running at the moment with the return BUT most of my corals are moving and getting a good flow. I intend on adding a second wp40 to it sometime soon. It all comes down to placement and angles in the end. You also need enough flow so that the sandbed is constantly being swept of matter so you dont have dead spots and stuff doesnt accumulate which can help algae and nitrates mulitiply.