Here are some points made—
** Kevin Timm says there's "less chance of blowing away in the wind" with a floorless shelter. Can't quite figure this one out as all shelters must be pegged. People who have a self-supporting tent with a floor and leave it unpegged just haven't learned enough yet.
** Justin Baker says " . . . one benefit of a floored tent is it's sealed off from water". This is a very important point—vital in fact. See below comments.
** Jerry Adams says "Set up tent, rain falls on it getting everything wet before fly is up." This is one advantage of the Hillebergs as they can be set up fly first with a hanging interior.
** But Jerry is right about one thing—"Only problem (with a pyramid tent) is if it's windy stuff can blow in under the edges." This happens with tarps too. This is especially true in open bald blizzards with 60mph winds and spindrift going everywhere and into everything—it stays out of a floored tent.
** Jerry Adams says, "If a site is flooded with a floored tent, water tends to get inside floor and then puddle . . . ." This all depends on floor denier weight and hydrostatic head along with the age of the tent. A good tent with a 70 to 100 denier floor(properly coated)—and a high hydrostatic number (7000mm or 10,000mm) will keep out this ground water and pooling.
Here's a test to do at home—Floorless folks don't have to do it unless they want to run this test with their ground cloths—
** Get a water hose and saturate a spot in your yard with water, making a small one-inch deep pool. Now, place the tent floor on top of this pool and sit on it for several minutes. If any water is coming thru then the floor is "inadequate". It could even be a new tent with a low denier floor (30 denier is common for UL tents).
This duplicates the real-world conditions of a deluge and finding your campsite swamped, which will happen on occasion if the rain is heavy enough no matter how careful your site selection.
Plus, this test can also be run on slushy snow and ice. Check the ground cloth too. Just some thoughts.