I was thinking more along the lines of a visual guide in the thumbnail. If on a project I'm asked to place an area of trees where the height of the trees was approximately 4m's (or whatever height), then while I was browsing my library I would have a quick guide of the initial height of the trees.
For example in the client specified a Beech tree, the HQ library has 5 different Beech trees so it would help if I knew the basic height of the trees in the first instance, to have a starting point.
I've quickly done 3 thumbnails to show what I mean. It means that if I'm looking for a 6m tree for example, it's easier to find.