I think it's only a must for Beatles fans with a completist/collection desire. If one buys all the studio albums, he-/she'll have everything except a couple of non-album songs on the Blue and Red albums. And one can take care of those songs with the "Beatles 1" compilation (with the exception of "Old Brown Shoe" which can be found on "Past Masters Volume 2" with good and great songs not found on either Blue, Red, or Beatles 1) that is much much cheaper than the Blue and Red albums.

-A Streetcar Named Desire-

Stanley: You want a shot? (offers liquor)
Blanche: No, I rarely touch it.
Stanley: There's some people that rarely touch it, but it touches them often.