While it is a usability improvement to be able to show or hide descriptions on the main admin page, it seems confusing to me that this show/hide setting also applies on the subpages 'admin/content', 'admin/build', 'admin/settings', 'admin/user' and 'admin/reports'.
As the main admin page is very crowded, it makes sense to hide descriptions there. The sub-pages on the other hand are less crowded, without descriptions they rather look like a uninspired list of links, and don't provide the information novices need.
Several solutions would be better than the status quo:
- To keep the generalized setting, but show the same "show/hide descriptions" link on every admin subpage.
- To add a "show/hide descriptions" link with a separate settings on each admin subpage.
- To always show descriptions on admin subpages, no matter what the setting is on main admin page.
2 seems to me too complicated, I'd prefer 3, but would also be happy with 1.