The rule in folk magic is blunt: add things while the light is growing, remove them while it fades. The waning half is for getting rid of.

Breaking habits, clearing out rooms, ending arrangements and, in older grimoires, undoing curses all belong to the fortnight after full moon. The symbolism carries it: letting go is easier to commit to on a night when the sky is visibly doing the same thing. Whether or not the Moon is involved, the schedule is.