This post isn’t about describing something nicely versus being mean. It’s more about how to best be direct in your description. I think of a “positive” description as a description of something that IS. A “negative” description, then, attempts to describe what something isn’t.
Her purse didn’t hold the normal wallet/sunglasses/keys combination.
His smile didn’t invite you to sit down for a chat.
The garage was remarkable because it didn’t contain a vehicle.
You get my drift. Sometimes, like with the middle example, a negative description is an interesting, perhaps voice-y or sarcastic way of getting your point across. The guy in the example isn’t happy to see whoever, and it’s obvious, no matter that he’s trying to smile. I’d buy that. The other descriptions, though, draw out the narrative because they are roundabout. Instead of revealing just what’s in the purse (a gun, say) or garage (alien laboratory, perhaps), we’re first told: “What you’re expecting to be in this purse or garage is, in fact, not in this garage.”
Well, yeah. If a gun is in the purse or an alien laboratory is in the garage, the reader will immediately know that this isn’t Grandma’s purse or Dad’s garage. So that part can remain implied, as all of our purse- and garage-related illusions are about to shatter.
Long story short, the negative description can sometimes be interesting. Sometimes, though, it’s more direct and less redundant to cut to the chase, cut out negative description, and describe what IS rather than what ISN’T.