To use it or not, that is the question.  Most of us have heard of this designation above somewhere in our education I believe.  It goes descending on C7 as ( C, B, Bb, A, G, F, E,D, C. )  The type of jazzers scale I prefer on a plain C7 chord goes like this descending ( C, Bb, A, Ab, G, F, E, D, C. )  Both scales have as their halfway note the note “G”, ( Fifth tone of the C7 chord and a strong note of that chord. The “G” ( fifth )is also a favorite “landing – note” for jazz improvisers.

Melodically, I find the version with the Ab in it more favorable.  In the Bebop version, sounding the B natural before the Bb, in a way, cancels out the effect of the flat seventh ( Bb ) coming right after the root ( C ).  It’s all a matter of taste I guess since early on Clifford Brown used the Bebop version extensively, while Harold Land preferred not to.

Basically – somethings become obsolete, or out of fashion – given enough time.