Mostly no. It's primarily a mental thing. That said, there are some circumstances where some sort of floor and/or liner is nice. E.g.:
Really bad bugs. In mild skeeter conditions not many fly under the hem, and must who do just migrate up and hang out in the peak. In bad conditions (e.g. AK range or North MN in June) a net tent is pretty much necessary.
Really bad ticks. I did a trip this spring in the Missouri River breaks and found a dozen ticks on my pants when I got to camp the first evening. I didn't get any on me overnight, but it did creep me out a bit.
Serious bog camping. I've never encountered a situation where good sight selection didn't keep my pad dry (I don't use a ground cloth of any kind), but it's conceivable that in a place like Scotland the only level ground could be saturated, in which case you'd need a good bathtub groundsheet.
Serious cold wind with no snow. If it's pretty windy, well below freezing, and there isn't enough snow on the ground to seal the edges things can get pretty drafty in a mid, even with sod skirts.