Some gaps users claim that due to visual impairment, it helps them differentiate windows from each other. I guess you could use larger borders instead but gaps certainly look nicer than that.

I have nice peaceful desktop backgrounds (e.g. pictures of mountains) that change every boot and I like looking at them. The gaps allow me to do that a bit and create some kind of persistence between the empty desktop and a desktop with a window on it. I do have two large monitors (one of which has almost no bezel and is lovely). On laptops I don't use gaps.

For me it's a bit like having a picture on a desk. It uses up space I could have used for working but I like it.

I think it's aesthetically more pleasing with gaps.