The one pad will get dirtier,faster than four pad's. In my mind,,I am trying to catch (filter) as much particulate with the mechanical media as I can.Flow and filtration are sometimes confused.
The more media that the water passes through,the more get's caught .
One could make the case that in properly maintained tank,no over stocking,no overfeeding,regular weekly water change,that there should not be too much floating about for media to catch,but most of my tank's are soil based and judging from those that aren't,,the soil based tank's filter's are much dirtier than tank's with plain sand,gravel.also have quite a few fish.
I have spare filter's if needed ,but with afore mentioned properly maintained tank's (my opinion),,the extra filter is not needed so I just switch out dirty one for clean one,relying on large plant mass to take care of biological filtration.
With lot's of plant's,,I can clean all media without worrying about losing bacterial colony.
might be dangerous in fish only tank's that aren't matured.