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I'm hiking, exclusively. Yeah, I get that perspective. One important disclaimer is that one generally doesn't need to worry about being stealthy in the U.S. One of the reasons I don't think I'll ever be able to move back to the UK is because of how how spoiled I am with public lands, especially in California and other western states. It really is crazy. I can camp basically anywhere so long as I'm following leave no trace principles. 30 metres away from water, 30m from trail etc.
I wouldn't consider a proper proper bivy because they're claustrophobic for me. For tents, I did try the Tarptent Double Rainbow and it was great to sleep in, but its pack size and the annoyance of carrying poles were the reasons I sold it. I went straight into the ultralight shelter end of things when I started hiking, so its the first shelter I'd had to carry dedicated poles with and I didn't like it at all. The pack size was also very big compared to what I'm used to.
The appeal of a tarp/net tent is exactly as @maki says - in the winter, flying insects are all but non existent west of the Rockies, but the weather is still really nice, so you can easily get away with just carrying a tarp and no net tent. The tarp portion of this SlingFin weighs 224g and as its nylon it packs crazy small. I don't know what nylon they're using but its been impressively resistant to sag versus other nylon tarps I've used like the Gossamer Gear Twinn.
After three days on trail I'm now staying at a proper campground in the Sierra where I could have a full size tent, but I'm using the tarp still and its been fine. All I'm doing is sleeping in it.
Are you riding or hiking?
I'm just thinking about bivvying vs tarps vs tents and still don't really get it.
Bivvy is faster and stealthier but you need to find some other cover if the weather is shit (or also carry a tarp).
Tents are better for shelter but heavier and least stealthy.
Tarps are lighter (lightest?) but less sheltered, less stealthy than bivvies and as slow up as tents.