Yes, and no. It is important to use your laptop on a relatively flat and lint/dust free surface. There are intake and exhaust vents which must remain clear of obstruction, or the internal fans cannot blow hot air out of the case. Likewise, the intake vent(s) can suck lint/dust into the case which will clog the cooling fins and etc. in time.
I would suggest a length of board or plywood long enough to sit across the arms of an easy chair, and sufficient for use elsewhere if needed. Otherwise, you are welcome to balance the machine in such a way that the vents are clear of obstruction.
Can I just leave it plugged in with no adverse effect, or am I supposed to unplug it when not in use.
As a general rule, you may leave it plugged in, though one risks getting a surge through unprotected cords (lightning strike, tv failure, etc).
It is important to your battery life that you DO unplug it from 110 now and again and let the battery fully discharge (till the OS asks for power). I do this once a week or so.
The last time I fully discharged and the OS asked for power was a while back. I haven’t been able to get it at least once a week since then.