Interesting question.

During my journey, I found that impact play and hitting are completely two different things. Simply put, impact play in BDSM is done consensually while hitting is not. There are initial agreement even contract between Dom and sub before engaging into impact play (or any other form of play) to make it consensual. Not to mention safeword. Hitting usually caused by a heated argument or a fight, thus does not involving any agreement, contract or safeword.

My thought about face-slapping; I like it. If it done playfully without any intention to seriously hurt the sub (I called it light-slapping actually). But off course, before I do such play, I have to make sure that my sub also like the idea to avoid any shock or mental trauma that might occur.

So, no apprehension for me at all.