Some taper up as they believe it to lessen the "shock" of using an androgen, though such is NOT necessary.
Also, tapering downward at the end of cycle is likewise unecessary. Contrary to popular misconception, down-tapering does not increase the speed with which natural test levels will return to baseline post-cycle.
The introduction of androgens places the body in a supraphysiological state, the deprivation of which will not elicit a compensatory response from the testes to re-iniate production.
Tapering doses will not aid in reversing HPTA suppression brought on during a cycle. If one has been on moderate-to-high doses of AAS and tapers, the presence of any exogenous androgen will continue to inhibit the restoration of natural tesosterone production (I am not here talking about "bridging" steroids or formestane).