If I liked the Anime then I would download the OST because it gives me memories of it :>
I have a bunch from Bleach :3 Asterick, Rolling Star, Tonight Tonight Tonight, After Dark, Shōjo S and also the OST's Invasion, On the Precipice of Defeat, and Number One x3 From Vampire Knight I have both the OPs and EDs: Futatsu no Kodou to akai tsumi, Rondo, Still Doll and Suna no Oshiro. Aand also from Black Butler the ED, Im Alive Lastlyy, from Death Note, What Up People!!
I have them as my ringtones and alarms too.
Sure, I get any music I like from the OP and ED of anime. I then use those songs as a basis to search around for more music by the artists, and so my collection grows and grows.
Want to hear my ringtone? No joke:
On youtube I actually made a seperate playlist for all my anime music
you know... for those times I just want to lisen to anime openings and endings and nothing else.