The reason for the Japa beads is so that you can keep track of how many times you are chanting Hare Krishna mantra daily. It should be chanted a steady amount of times regularly. We chant at least 16 times around the string of 108 beads daily (one full mantra on each bead). This keeps us strong in spiritual consciousness.
Letter to Mr. Lourenco, 14 March, 1975