How many resources does an empty OSX desktop take?
Quick unscientific testing says: not enough to be significant.

I increased the number of desktops from 1 to 16 (which is apparently the maximum), and kept an eye on the memory usage of WindowServer – it went up a few MB. CPU seemed unaffected too. Definitely neglegible on any modern hardware, and far outweighed by the resource usage of programs like Firefox, which is in the hundreds of MBs.

If you enjoy the extra space, by all means go for it.