Hi Sheila @sheila5 ,
That GPU Subdiv is not necessary; I leave it off.
If you have a Subdivision Surface Modifier at the bottom of your Modifier stack, it will be a bit faster (depending on your GPU). In a heavy Scene, with lots of Subdivs (at the bottom of the stacks!), that GPU Subdivision can speed things up, but I don’t think it’ll make much difference with only one or two Subdiv Modifiers (don’t have any numbers/statistics).
