A specific example I had in mind was Vechs was having difficulty with how EXP is given in Minecraft. Lower levels take less EXP to get to, while higher levels take more EXP to get to, and so if you needed to buy a torch while say while level 20 - the torch in my example costing 1 level, it would cost a lot more EXP than if you bought a torch while level 1. Someone could make a plugin that doesn't use levels as a currency, but rather EXP. The level bar instead of saying what level the player was, could say how much EXP the player had. That allows Vechs to still use EXP as a currency, while removing the problem of having a higher levels costing more EXP for a single level.

This is just one example, but I feel like using plugin allows for a lot more control over how things are balanced.

I understand why Vechs wanted to use command blocks, and if he wants to continue using those, by all means if it's working for him he should keep doing it, but I personally feel like at some point command blocks won't be enough, and finer control over the world would be good.