On the couple of occasions I've shit myself in my adult life it's been unexpected and inconvenient in terms of cleanup etc. That's the one downside to it.
I do, however, find the idea of a woman filling her panties/knickers something of a turnon. It dates back many years to an incident during which my (sadly now late) Aunt Anne nearly shit herself whilst visiting after sitting and farting for ages. Why she did it I don't know, but Aunt Anne put off excusing herself until she was nearly pooing herself. At the time she was a fit, attractive, 37 year old school teacher so I thought it was hot. If my memory serves me, she was wearing a tartan skirt at the time.