Even though I have done a few high temp cooks I have not had a problem, probably due in part to the short duration of those cooks. Plus I keep my pit clean for each cook, so I haven't had a grease fire, yet, and I would very much like to keep it that way.

Like most here, I do it frequently when doing long cooks. No problems so far

Leaving the pit unattended was the excuse, err I mean logic, that I used to get the wife's permission to get a tappeque! 

Done overnights on my Yoder 640 mebbe 20 times in the last three+ years.  I clean my pit somewhat between cooks.  After a batch (6) of pork butts or 9 chickens I do clean.  I do a major clean with hose once a year.

No issues.  Smoker is within 3' of a house wall, under a aluminum patio cover.  Use a dry vent tube to direct smoke above the roofline.

Than God no issues.

 Any house hold insurer would say no unless the pit was in a fireproof location..Three things come to mind.

1/ Restart w/ an overloaded burn pot. Could happen w/ auto restart.

2/ Grease fire.

3/ Hopper burn- back. All these are fire issues.  Some pits have some protection of sorts such as high temp shut down.

 If you view my post on, What is the Most Stupid Thing You Have Done, you will find some valid reasons why to pay attention. Some of the best

of us have forgotten the simplest things, the results not being good.

 A Big Green Egg owner left the lid of the egg open to cool off after the fire had died-NOT. The side of the house was destroyed when the

charcoal came back to life.

So it isn't only our pellet pits that are potentially dangerous..
 

I do this quite often. If you check the weather, place the pit in an open space far away from any flammables, make sure it's powered from a GFI/breaker protected source, keep the temperature relatively low and only put as many pellets in the hopper that you anticipate that you will use for the time your gone, you should be OK, even for over night cooks. The worst that could happen is that your pit burns up, the neighbors get a free fireworks show, the fire department gets some exercise and you get a new pit. 

This is why I like my fireboard. If temp gets to low i get a text. Too high I get a text. I don’t usually travel more than a few minutes away while it’s running though and I usually clean out the pit every 20 lbs of pellets burned.