Now, this may sound like a dumb question, but hear me out.
For CFrame, if you do it on the Server it causes stutter and delay / choppy CFrame.
However, on the client, it is very smooth and should be done on the client.
Is this the same with GuiObject Tween? (SurfaceGuis)
From what I have seen ingame with games that do this (like Pinewood Builders Computer Core, a pretty server-intensive game), the TweenSize and TweenPosition functions seem to be replicated to the client where the client actually locally tweens the objects. The probably should be tested though, with some type of synthetic load on the server to where it runs noticeably slow, or doing print(1/wait()) gives a number below 15.
do it on the client