I keep mine in the garage, so never.

Living in Oregon if I kept it outside like I did the gas grill it would have a Mel's or similar cover. Gas grill looked brand new when I got ride of it.

mudflap

 My input now as I didn't want to influence the answers.  My covers are well made, don't leak, for the most part easily installed. As with all covers, one drawback is don't install on a hot or wet pit. The ceramic komadoes are a bit of a pain, taking 2 to 3 hours to

cool down... A few years back I had a cheap cover that lost its flex-ability in cold weather. That was a major deterrent...  The reasons I cover are ,weather protection and to keep the cookers clean. Even tough they are stored and used under cover, the elements

have a way of getting on my beloved pits... In the end I find it less work to cover..

Thank you to all that have imputed so far. 

I discovered a mouse nest in my pit a few years back.  The cover almost reached the ground and provided a way in.

There's usually no reason for an unduly long cover.  The parts I want to protect are normally up high, so leaving the legs exposed isn't generally a problem (mice don't seem able to climb up metal legs).

It also makes the cover lighter and easier to put on.  (I don't have Bentley's upper body strength and Mel's covers are HEAVY.)

I'm surprised it hasn't been mentioned yet, but pits with Traeger-like smoke stacks are an absolute pain to get the cover on and off again.

DK 

All the time.  I can't bring myself to leave a $1200 smoker with electronics uncovered when not in use.

I've been cooking with pellets for 10 years now & still feel this way no matter what the cost.

A

I cover the next day after cool down which is usually late in the day.  So next AM unless I'mm cooking or a major cleaning.

So, yes I cover all the time.  To keep the Vegas dust off mostly.  And keep the dirty girl (i'm not a spotless griller, it's a grill/smoker right?) Kinda presentable....

A  it's stupid dusty in the Phoenix area and I try to keep the grills presentable and clean. 

I'm surprised it hasn't been mentioned yet, but pits with Traeger-like smoke stacks are an absolute pain to get the cover on and off again.

DK

Yes, that and the stupid grease bucket.