Just beforehand is to relax you cervix so that it is ready to accept emby, and afterwards is to ensure that enough blood flow through and will hold emby. Good luck and let us know how you go.
I am a firm believer in a/p. After 10 years and 6 cycles of IVF, we managed o get a BFP this year naturally after 6 months of a/p! it was the only thing that we had done different in the 10years of trying for a family! good luck and definately worth a session before and just afterwards!

take care and good luck

odette