Just think about it this way - Does the mod give you an unfair advantage over other players? Does it give you an advantage that other players would normally not have?
Mods like OptiFine don't have an unfair advantage as they increase computer performance, so that is why they are allowed. But mods such as Aimbot give you an unfair advantage, as you can strike a player with your sword or arrow almost every time perfectly, a move that not even the best of the Senior PvPers can probably do.
If you're still unsure about it, I'm sure the senior staff will decide for you. Being a former mod, this is normally how I decide whether I should use a mod or not.