As said it all depends on what it is and what's in it.
I have a 2.5 gallon glass cookie jar sitting next to my head on a widow sill of the kitchen. No fish just pond snails. No filter No heater.
Bottom is a clump of java moss. Top is capped with Ricca that needs to be thinned out and a clump of java fern floating under the Ricca.
Tank is the easy one of the three I'm keeping right now. What surface scum it
s all Ricca.
Any how take a look at the circulation = tank health question I asked a couple of weeks ago. This may answer some of the questions your looking for.
What I'm finding is exactly what is suggested here. System is fine and dandy till it over grows itself and the body of water turns stagnant...foul. rotten...
For me this is my high tec tanks right now. It's time to source another canister filter for the beast.
So in some cases it's nice to have a low tech do nothing grow out bowl.