As it says on the tin, some users wish to set the specific date that they are charged (IE to the 15th, or the first etc. Allow getting the date that they are expected to be charged, as well as updating that date, so that the user is invoiced immediately, and then will next be invoiced the anniversary starting from that date. This can somewhat be emulated via removing and re-creating the subscription, but that can cause problems with recurring metrics resetting when they are not supposed to.