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

One if somewhat temporary.

Both if I want 1-2% increase in performance.

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

Just one on each end.

The real answer is the top one fell out a long time ago.

That one standoff got loose 12 years ago, so none.
Otherwise, it's all HDMI and DP.

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.

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

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

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.

I plugged one in today. I left the screws loose. Ironically I moved it between two computers that couldn't originally do VGA.

I re-organised my leisure desk. My C64 sometimes hooks up to a TFT thanks to my turbo chameleon 64 cartridge.

Today I hooked my C64 up to my CRT instead. I needed that TFT for my Amiga 1200 which has DVI-I out thanks to my indivision flickerfixer. But I have a DVI->VGA adapter to use that same cable.

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.

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.

Serial cables. How quaint.