This can be used for a host of things. I personally use this with Workflow for iOS. When I use my Log Caffeine workflow, a dropbox text file is updated, this update is logged to my google calendar, I can then see what times of day I partake in coffee!

This Trigger fires every time any file is saved in the folder you specify. NOTE: will process up to 15 files per polling period.

This Action will add an event to your Google Calendar. Simply include a detailed description of when and what.

Add Dropbox File updates to Google Calendar