I have an Ender 3 which I primarily use for printing with PLA. I haven't branched out to other materials yet. :)
I've done some research into PLA fumes and airborne particulates which seemed to mention that PLA is mostly safe, but ABS is rather dangerous to print without proper ventilation. However, I understand that there isn't much research on the topic and that there haven't been many studies.
I have been keeping my printer in my bedroom, far isolated from flammable materials, which I sometimes leave on to print while I'm asleep. Should I be concerned with my health safety with respect to airborne particulates emitted by printing with PLA?
Other questions ask about ABS, but here, I'm asking specifically about PLA.
Fire is the most obvious risk - firmware can now detect some of the more obvious failure modes such as a detached thermistor, but loose or failing connections can still overheat. A smoke alarm is a fairly obvious (but not necessarily effective) protective measure.
The risk from particulates in particular is probably low, but marginal health risks like this are extremely hard to analyse, and will likely take many years to manifest. The closest analogue would be to look at commercial plastics workers since they are exposed to both heated plastic, and any potential dust generated.
You could also compare the risk to other 'hobby' activities such as soldering, painting, woodworking.