Yes on both accounts.
Item links presumably preclude external MD editors from displaying the image(s) in preview, and the link doesn’t tell you anything about the image that you’re using (whereas you can use speaking names with assets).
But converting links to item links only to be able to remove unused images seems to be a bit convoluted. You’d have to script the conversion from link to item link, so why not write a script that removes unused images in the first place? And, again: Why are unused images an issue at all?