Floorless shelter in the rain?

Most common set-up in rain?

Tarp, Bivy, Groundcloth, and misery. The last one's free, and light!

I use a bivy in my Duomid. No worries about tracking mud all over the inside that way. And the important things stay dry in the bivy. I can cook in there and spills are not a problem either. With a tarp, if large enough a groundsheet would be ample.

When using a bivy is a ground sheet really necessary?

I don't use one with mine.

We use our Oware pyramid in rainy season here in Southeast Alaska. Rainy season is real rain, not sprinkles, its the Tongass Rain Forest. Rest of the year its tarps. The beauty of the rain forest and beaches is that there is seldom standing water, the duff soaks it up fast and all it takes is some thinking about location to set the pyramid on dri(ish) ground. We use tyvek ground cloths in the fall and a small (5×7) tarp in the winter.

I think the same strategy could be used anywhere. It’s all about where you put the pyramid or tarp.

First time i tried one i was sold, and i sold my double rainbow too.
I used a Twin sisters a kifaru paratipi and a shangri la 5.

You can enter and leave your shelter with boots on, you set up the dry part where you will sleep on only when wanted.
I use either a groundcloth or an inner ( myog for my paratipi, pyranet 3 from bearpaw with my shangri la 5) as we were 2 too and now are 3 so its both lighter and more friendly than separates bivys.

Regarding:
"Tarp, Bivy, Groundcloth, and misery."

This is true when done incorrectly and not for a lot of people.
Most people probably pitch their shelters in bad spots because they assume their bathtub floor will protect them from pooling water. It only takes a pinhole for the bathtub to fill up by morning.

Ironically, the people who would never use a floorless shelter are the people who complain about the leaks in their bathtub floors.

I personally find floorless shelters more comfortable.

I have pitched during rain and woke up on an island surrounded by water. I was relatively dry because I thought about where I pitched.

Benefits of floorless in the rain are:
Condensation is less of an issue as the water runs into the ground rather than collecting on the floor.
Safer to cook inside your shelter. I'd never do that in a floored shelter.
More pitch options. Pitch low to block drafts in cold weather. Pitch high on hot summer evenings.

Various ultralight bivys are equivalent to a bathtub floor and bug net, protect your bag/quilt and can be comfortable. The combination means you don't have to pitch a shelter if there isn't much chance of rain or snow.

"I personally find floorless shelters more comfortable."
Yes, I agree.

It depends on where you camp. In many campgrounds, you don't have a lot of choice. So, a bathtub floor makes a lot of sense. Often a good base camp, even if it can turn into a muddy mess at times. Out hiking, it is different. You do have a choice. A small mound or slight grade over a dip can make a big difference. On already wet ground, well, thats why a good pad and/or a ground cloth is often needed.

I use a pyramid, like the oware

And a bivy

It makes no difference that it's raining until you have to pack up or go out for some reason

You need plenty of headroom so you can sit up and move around

You need enough floor area for your bivy, and some gear, and a place to cook

Like a "4 person" tent for one or two people

A "bathtub floor" catches any water so it can get your stuff wet – I don't want to take a bath