My very first printer was my daughter's - it was a Monoprice Cadet that was a great introduction to the hobby. Although it wasn't a hobby-grade printer (like the Enders) and didn't include replaceable/upgradable parts, it showed me the parts of a printer that are most valuable when considering my next one (stuff like heated beds, auto bed levellng, etc). Unfortunately, one day while printing, I just happened to check in on it using my camera and saw smoke/flame whisps coming out of it. I ran down, unplugged it, and fire-extinguished it. It looks like something happened to the thermal couple and it just melted the whole extruder cage/wiring.
Now, I had been running this thing like 16 hours a day for over a year; that's a LOT to ask of a $99 printer. So that dropped me down to 1 printer; my current Ender 3 v2. My v2 is considerably safer since it includes a few more firmware-based protections. Unfortunately, I have had one issue with it about 8 months ago where thermal runaway happened on the nozzle but it did NOT SHUT DOWN like it was supposed to. Luckily, Octopi (the software I run my printers on) notified me, and I had to run down and shut that sucker off ASAP. I replaced the entire extruder at this point, and haven't had any issues since.
I personally NEVER run these when I am not home. And I NEVER run them when I am sleeping. I only run them when I am around and can actively intercede if I see them having a problem or if my smoke alarms were to go off. I'm lucky because I work from home, so I can pretty much run them 16 hours a day to get through the massive amount of requests that I have.