maybe it’s a matter of preference and the way one handles information, but i've always found it extremely important. so important that i never add files into my library unless they're tagged with some form of cover art. being, i'd say, a very active consumer of music (i.e. one who very frequently acquires/adds new music into his collection, on a near-daily basis), i rely heavily on the ability to visually identify a track or album. for me, the absence of cover art would significantly cripple my capacity in discovering, managing, and consuming music (even within my own collection)..

for artists i'm most familiar with its less of an issue (though even then, if they’re active with releases and/or have a large volume of singles/loose tracks, identification by cover art is the quickest way for me to find a track or narrow-in on one within an album).

but for newly-discovered artists and/or recent releases (soundcloud’s primary focus) i find it absolutely crucial as i’ve found artist names and track/album titles to, in fact, be generic, interchangeable, and often forgettable -- at least until some degree of familiarity is formed. filtering by genre and release/acquisition date helps to some degree, but even then you’re left with a lot of names/titles to remember and associations to make; having the visual representation cover art provides makes this all much easier to manage, for me at least.