Nope. It's an idiots safety precaution is all. Static electricity is nothing more than a difference in charge between 2 objects. So the case sitting on a table has a certain charge built up, you standing on the floor has another. When you touch the frame, that charge equalizes. An anti-static band, mat etc does the same thing, except constantly.
So as long as you touch the frame before inserting anything, every time, you are good. The idiots part is when ppl forget to touch the frame.
Me personally, I'm lazy and meticulous, so I lean my forearms on the frame when adding/doing anthing inside a pc. Problem solved.
Is one necessary? No, not really, is it worth the money? No, not really. Can it save your butt if you forget to touch the frame? Most probably.