Often the riggers skin a low res character and use it to drive hires version of character with SkinWrap modifier.
When you use SkinWrap, your driver object need to be Mesh object. If it is not, it will convert to poly under the hood. The mesh <> poly conversion price is very high.When I tested this originally in 3dsMax 2014. The test result was 9.75fps vs 17.89fps. I retested other file in 2021.3. The difference was 10.8fps vs 13.1 fps. So, I guess there has been some progress. It is still taxing 30%.
Skin modifier doesn’t care about poly or mesh. Therefore, if your base object is Editable Poly, just apply Mesh Select before Skin. You will get performance boost.