So, your question is referring to the hammocks that don't have the bugnet built in/separate bugnet system? ....or are you referring to netless, meaning just that, totally netless...like going without underwear?
To address it all on my point of view:
I must, must, must have a bugnet. I don't like the thought of being ate alive by bugs while I try to sleep....and not one of those bottomless bugnets either. Those **** forest floor spiders jump, grab on, and climb in with you. A total nightmare
The bottomless is now my "lending bugnet"
I use a seperate bugnet, for several reasons. I can dangle my foot over my hammock if I want to, I can dramatically change my suspension lay and ridgeline if I need to (do to hurt hips or back), I don't have to pack it if it's not needed, I can switch it out for my overcover/sock if need be (and not have to mess with 2 separate things). My hammocks are wide enough, and foot box deep enough that my TQ doesn't fall out, so that is not a problem for me. Even when I was using my Eno DN, I didn't experience problems with my TQ falling out.....and I'm not a small, short woman. I can also use it on more than one hammock.