My feeling is similar to that of aimless. I've used a light (water "resistant", not really water proof) bivy in conjunction with a poncho/tarp in situations where I didn't expect to deal with lots of rain, as a flexible weight saving option. Perhaps the state of the art has changed, but for a bivy to keep you reliably dry in significant rain, they can get to be as heavy as a full tent, and much (much) less comfortable and flexible. I used to own a really waterproof bivy, one that had a little flexible pole to keep the fabric off of your face --- it was I think as heavy as my sil-nylon single walled tent (I gave it to my daughter when she got into search and rescue).

Having a decent amount of dry and bug-free interior space is very nice, especially when conditions make you want to be in there. I've had situations where the bugs are out in force and I was too warm to be inside my bivy, even putting my body on top of rather than inside of the sleeping bag.

Where a bivy shines is in limited space situations where perhaps there are challenges to pitching a tent. So if you expect to camp on the side of a mountain, or you go caving a lot, or use it with various snow shelter options ... that sort of thing.

But some of the issues come down to "personal preference". Ideal would be if you could borrow or rent a bivy and try one out, hopefully either in fairly benign conditions, or close to a trailhead --- or in your back yard.