I've tended to assume that many, and possibly most, spanking enthusiasts are also lovers of panties. Certainly the two go hand-in-hand for me, and I've administered many a spanking without ever removing a lady's underwear (but also many more that
have ended with a bared bottom).
In terms of 'realism', then I'd say a true punishment scenario should be no-nonsense - panties down even before the first blow is delivered. But of course, that does preclude the fun of the 'unwrapping', which as others have said is often highly erotic for both parties

.