I use the Layers Panel all the time. The panel helps me navigate complicated illustrations and helps me find, select, and arrange objects. The Layers Panel is surprising customizable, adjusting to how you work. Creating large thumbnails adds to the functionality of the Layers Panel. Moreover, you can get rid of the thumbnails, or even keep thumbnails on the top layer only!
I’m pretty sure this feature is available in the other CS versions of Illustrator. If anyone knows otherwise, let me know!
Layer Panel Options
Open the pop-up menu of the Layers Panel and select Panel Options at the very bottom. Here, you can set the thumbnail size up to 100px or get rid of the thumbnails altogether. Check out some of the other options and customize the Layers Panel the way it works best for you!