A few years ago I camped in Koke'e State Park, above Waimea Canyon on Kauai, and on New Years Eve the rain ultimately angled at about 80° to the ground with sustained winds of 30+mph. The wind direction shifted a good 90° halfway through the night. We were on sloped ground well away from the lowest point, but when we awoke even the slopes retained 2" of standing water.
In such conditions, a bathtub bottom tent made all the difference. With the wind shift, a freestander can just be unstaked, rotated, and re-staked. We were sleeping in a river - there was nowhere that wasn't! Groundsheets would have been overrun by the runoff.
So, all told, for me there's sometimes a benefit of even an UL tent in UF conditions, to speak nothing of the mental benefit/comfort, which is entirely more subjective. Now that rain's returned to us here in Northern California, this sure is a timely topic...
Fun to see everyone's varied opinions on this interesting topic!