Some artists use subtle sensuality on their album covers to convey a certain aesthetic, others blatantly hammer home the sex appeal with gratuitous nudity.
Just as an album's opening song plays a pivotal part in a record's cycle, the closing track serves a similar and not totally unrelated purpose.
In a way, the final song is the summation of an LP's musical and thematic themes, a final word on the past 45 or so minutes...
One-hit wonders are a dime a dozen in rock music, but to be able to come up with a single great song and then stick it on an album that's otherwise terrible?