Sump design, and pump size have a lot to do with the type fish kept.
If you want fish that require heavy flow, like some more high saturated oxygen using Geophagines, or rheophillic Central Americans, the sump might need to be large enough to handle more water volume, and heavier flow, without sucking dry in certain situations.
When I was using a 40 gal sump, but a 1000 + GPH pump, I was always worried some anomalylike a plant plugged drain pipe or..... would create a dry out situation.
This is why I now use a 125 gal tank as my sump/refugium.
I also don't use baffles, except a porrett foam barrier to separate the pump/biomedia area, from the larger refugium section..
My fish are riverine, so I like a lot of flow.
If I was keeping ox-bow/placid water species, I might skimp more on the pump, and sump size.
But when in the states, I often ran up to 5 tanks on a single sump, so my pump preferences were always on the more powerful side, and I could regulate strength of flow to different tanks with only a valve on each tank.
I always wanted the option to go up or down, according to a changing situation. One size doesn't fit all
That's also why I didn't use permanent baffles, that could restrict change, and also got in the way when doing maintenance.
