I remember the first time a tenant unplugged a refrigerator before moving out, probably to defrost so they could clean it. It was clean so I didn't think anything of it and just left it unplug a few days to move around easily while painting. But as mentioned there's those little crevices that they bypass or don't remove all the shelving to get at they just wash the exposed surfaces. Needless to say a few days later upon opening the fridge I was meant with tons of moldy black dots everywhere. It didn't take long for that to develop. What seemed at the time as one less task I had to do became quite the job removing all those moldy dots, especially in the crevices. First thing I do now when someone moves out is make sure the fridge is still plugged in.