If a watchface has customer setting like color changes etc. this goes lost after smartwatch restart or change of the watchface. So it where nice if can set global variables they are stored on the smartphone to outlast this. Also it where possible to use this global variabe in the feature on the phone to allow the user of the watchface to change settings there. Also if the watchface is protected.
For example. Watchmaker have a small userinterface (defined from watchface creator) on the phone over there can set some default setting over the global variable.