I use 8 desktops on my MBP for my different apps. Do you know if it can affect memory use?
Look at it in another way: You don't have 8 desktops but you just have 1 desktop. The applications are bundled into groups and only certain groups of applications are shown on your desktop screen. When another application becomes active from another group, then the selected group will become active on your desktop. It feels like your have 8 desktops but in fact you only have 1.
So to answer your question: It will need more memory than a static desktop but I doubt it's even Noticeable.