takes up memory ?

[Dae'lomdel]

It should be obvious...

Of course if you HIDE the UI your going to get better performance... good luck playing with no UI.

The real question is "Does a cutom UI lag you more so then the Default." and the answer is there is no real way to test it perfectly, but if there is a difference in either UI's favor its so minute that it does not matter.

If you are worried about performance with UI, having less windows open... regardless of if its defualt or custom will cut down on a tiny bit of the resource usage.