Thank you.
Using a midi clock is new to me with this board. Previously used a Disaster Area DMC-4 to control my midi devices and sync up tempos on my delays, where needed. The Quartz allows me to pre-program tempos for individual songs, with the flexibility to adjust on the fly. (Check out the Goodwood YouTube video on using the Quartz with the PBC.)
While I could probably do this with the PBC alone, the Quartz frees up a button on the PBC and gives me a few more options to play with. Probably not a "must have" pedal for all situations.