For a very short period, I continued to use the Quartz after moving to the PBC to handle BPM and Tap Tempo duties.
The reason - it was familiar (I used it previously with the G2 switcher), BPM was always visible, could be quickly adjusted, and I didn't need to do any menu editing/button presses to get to my delay page on the PBC. As I grew more familiar with the PBC functionality and downsized my board I built the clock/tap tempo functionality into the PBC and dumped the Quartz.
I do miss having the tempo read out from time to time but that's not something that detracts from my performance... more of a safety blanket or convenience factor when I need to tell someone else in the band what BPM we're on. Having the current BPM visible on the bottom right of the screen (opposite the loop indicators) would solve that.