In most cases, the reason people are posting on here is because they have a problem. We are trying to help them solve that problem. If that means telling them that a common pleco doesn't belong in a 10 gallon tank, then that is what they need to know. If you have a small common pleco (3"), a small oscar (5") and 6 neons (6" total) in a 20 gallon tank, you probably don't have a problem NOW. But give it 2 or 3 months till the pleco is 6", the oscar is 8", you have a ton of waste from them and your neons are gone because the oscar ate them. THEN you have a problem. That is what we are trying to help people avoid.
Edited for spelling.
Edited for spelling.