Is this an 'old wives tale' about underwear or has this happened to you?

Without fail, my mother always use to say “be sure you have clean underwear on, in case you have to go to the hospital”. To me, this is like saying it’s going to happen and you be sure you have on clean underwear. Question: so, is this saying more fact, than fiction and has it actually happened to you? Should we always wear clean underwear, just in case we are injured and have to go to the hospital? Do ER workers even care if we are wearing clean underwear? Or, is all of this just an old wives tale?