Yes, yes I know falling sand and gravel causes lag, but what if you turned the ability for them to fall off? I know you are able to do this because I have done it myself in the past on my own server, so please consider this because some builds require a lot of sand or gravel and it's not fun to have to do it by hand.
The plugin is anti gravity but i think that plugin is broke with 1.9 there is a way to use sand and gravel in world edit just use //copy and //paste anti gravity is buggy in 1.8 too.(Copy and paste is for VIP+ or you can get 1 hour free by voting 10 times or something like that and doing /voteshop)
I can tell you the issue with this. Blue said that anti-gravity works by intercepting the event where sand turns into an entity and blocking it. The problem is that the event is simply called again and it has to be constantly blocked. This causes lag in and of itself.