To determine whether or not any fish "needs" a wave maker.
Although ........."Need" is a bit of a relative term
Look a videos, or photos that show what the natural habitat your particular fish lives in.
Does water move in a linear fashion? Is the fish riverine, or does it prefer sedate pools?
If they come from environs that look like these......they probably "need" a wave maker
I keep fish that come from habitats similar to the ones above, so beside the flow from my sump.
I add wave makers half way down the side of thank where flow starts to ebb..
But if the fish you keep come from waters like the two shots below, the term "need" may be an overstatement.
Then again, if their natural waters are similar to the moderate flow below....
A small wave maker that adds extra oxygenation may also be advantageous.
And can come in handy if a filter gets plugged, and slows, or fails, it can take up the slack until the main unit gets fixed of replaced