Both, three rotations after the threads catch.

One or none bears the risk of the connector coming out crooked and bending the pins, causing a potential alignment issue on the next connection and bending them further.

If it's for more than a minute I'll screw in VGA and DVI cables

Both. If there's a screw, I'm tightening it, baby.

When I used them, I screwed both in usually.

Neither. Trip hazard.

Serial cables. How quaint.

I've always screwed them both in very lightly

I think this is highly dependent on the setup.. like is this temporary, semi- temporary, or permanent?

It depends.

For my work computer, I screw them in tight, both on the monitor and the DP/VGA adapter.

For stationary devices (like overhead projectors) and extension cords, I screw them in, but not very tight.

For classroom computers, I only screw them in on the monitor and leave them unscrewed on the computer. Students can't keep their legs calm and often snag the cables. I prefer to let the connectors harmlessly disconnect instead of damaging the graphics card or motherboard.

I don’t screw them in unless it’s in a confined location where the cable is applying pressure to unseat, or if it’s fallen off at least once

I sure wish my external HDDs had screw in ports. Those things come loose if there's a change in air pressure.

My current job, we test products with these cables, we are required to screw in both when plugging it in, so both.

Neither, and I never once had the cable fall out. Just imagine the countless seconds I saved from not screwing and unscrewing.

if I HAVE to use vga, and its only being used for 1 computer, than both, else none if im only using it for temporary reason , none.

It depends.

When the VGA socket I'm plugging the VGA cable has a screwing hole (for example, tower PCs as well as some HDMI-To-VGA adapters) , and I'm intending to let it plugged, I generally do screw them in, not entirely, but sufficiently to don't let it escape due to VGA cable's weight (especially if the cable has dozens of meters as well as those cilindrical magnetic thingies that reduces electromagnetic interference).

But one of my laptops have no screwing holes at the sides of the VGA socket so it's impossible to screw the VGA cable.

Context kind of matters for me, but if I'm screwing any in, it's both of them.

My monitors are on a swivel bar, and plug into the underside. Those get screwed completely in if the cable has screws. But on the desktop, since it doesn't really move and I've never yanked a cable, they're usually left loose.

Oooooh ! You !

I usually screw in both bolts but I still have an old laptop that I use on very rare occasions that doesn't have the screw holes for some reason.

Both, but the second always gets stuck before the end.