Player choice is important. Every mod should have very detailed config options to allow any type of player to enjoy the mod. If it floats your boat to make a bucket of UU matter with 1 EU, you should have that option.
On a multiplayer server, it is different. If you are using an "overpowered" mod, cross-mods, exploits, etc, then it affects the other players on the server. For example: You are using a mod capable of duplicating blocks within a week of playtime. The other players are using mods that take a month to duplicate blocks. You have an enormous advantage in this situation. Your massive growth will have an impact on the world and server economy.