I just moved my computer from its prior setup under the desk to one where it is on it (albeit a different desk), so that it's easier to access the ports on the back and to make sure the vents are clean, (I also removed dust from the vents, opened the case to find that the CPU cooler had fallen off, and put the cooler back on; system now idles at 40C instead of 50C.)

So, how is your computer set up? Is the computer on the floor, or on the desk? Do you use an external monitor (or multiple), or do you use the internal displays that some computers (particularly laptops) have?

I have one laptop, this one where I am writing this, on a big desk in a bedroom (where no one currently sleeps, even if there is a bed here; I guess one of my boys will sleep here when he grows up a bit).

Another laptop is in the living room corner, inside an IKEA computer cupboard. I don't use it that often (when it is in that cupboard), but one of my sons regularly plays TeamFortress 2 on it. He calls the game "down-pew-pew" because obviously you shoot in the game (hence "pew-pew"), and he likes to play certain maps where there is lots of elevation and you might fall down from high cliffs or towers (hence "down").

There is also a very old, 1-core retro-gaming desktop PC in that same cupboard. I rarely use that machine though, no need. It might be needed for some old retail CD games and such that can't be run on modern PCs.

Then I also have one older laptop sitting on the coffee table in the living room. I quite often fire that up if I go to see the TV and want to do some stuff on computer from the couch at the same time. I've learned though I don't multitask that well, if I start doing something on that couch laptop, I usually lose track of what I was watching on the TV, ie. not understanding the story anymore as I haven't really been watching the movie going on the TV etc. It is good for reruns or TV news where it doesn't really matter if I miss most of it.

So long story short, quite interestingly I hardly ever use my laptops on my lap. Usually they rest on some flat surface, a desk or a table.

I have my computer plugged into the wall....

MATX tower on the floor + 27" monitor. On vs under a desk makes no real difference to temperatures but under a desk effectively places the case a little further away from the ears (plus uses the desk as a sound barrier) which reduces perceivable fan noise by a few db. And having grown up with those beige AT behemoths that sat underneath an equally chunky CRT monitor, when we switched to TFT the main reason for the trend to move to tower on the floor was completely freeing up desk space. I'm not really sure I get the current Mini-ITX trend of "saving space" by putting wide square cases back on the desk again (taking up useful desk space) when under a desk is typically space that isn't used for anything else.

The problem I have with "under the desk" setups is that it's not so easy to access the back of the computer, which is a problem if you need to access the ports (USB or otherwise) there. Also, cleaning out dust from the vents isn't so easy when it's down there.

I have a laptop. Sitting comfertably in the sofa playing

I have a setup that I consider rather garbage, I use a old school desk as my desk with my computer on the floor next to it. If I had a choice my desktop would be on a table. The desk isn't big enough to have my keyboard and mouse pad not to overlap.

But my mom won't let me actually work on a better setup... so I will be stuck for few years with this bad setup.

Both PC towers under the computer table. The one on the left is my gaming rig, the right side is my everyday use rig.I have a 34" ultrawide monitor attached to the gaming rig and a 24 inch monitor attached to the other one. I don't worry about USB ports in the back, as I have enough on the front of the towers and my keyboard has some as well.

Wait, what?

How the hell did that happen? They're usually held on with some heavy duty clips or screws - in 30 years of building and maintaining computers, I've never had a cooler just fall off. I'm guessing the clip somehow sheared off when it got jolted/moved?

A wave hit it.

I've always put my desktop computers on top of a desk. Since a couple of years, I've started cleaning it out (with a compressed air machine) every two years. Still, it's a chore and I try to minimize chores as much as I can. Desktop cases under a desk just come into contact with a lot more dust (from the floor).

Some people like cleanliness enough to clean their place* once or twice a week. Me, of course I don't mind it being super clean - but I really dislike chores - and they take time away from what I really like doing in the limited time I have on this earth.

*explanation: cleaner floors = cleaner PC on the floor

Edit:
- These days, the sound/noise is irrelevant. We both (me and my SO) have quality cases with relatively modern parts in it. You can only hear them (light zooming) when there's no background sound. It wasn't always like that.
- I don't get the difference of accessibility between under the desk and on the desk. In my experience, it's (mostly) about the distance from the wall. Edit2: And the distance between the left side panel and any obstacles.

Or I might not have fastened it securely enough when building the computer 8(?) years ago.
Don't forget that bending down is uncomfortable for many and not a reasonable option for some.

Those people probably bend down A LOT more (e.g. to pick up something from the floor) for other purposes than to reach behind their PC, or open it up. If bending down is an issue to regularly plug in/out USB devices - just connect a USB hub.

yeah , don't put it on the desk , it just takes up valuable space there from food and drinks

imho the best is to screw it up onto the ceiling , the cables run down behind the monitor