This functionality was introduced in vtiger_crm 5.2 and respected in coreBOS, it is probably documented in the manual. The behavior is to increment the "Used Unit" field and calculate the "Progress" depending on the "Tracking Units" and the related trouble tickets. If tracking units is time, the time on the support ticket is used, if not the ticket themselves are counted.
This functionality was always on, what we did is give the option to turn it off without having to go to the database. Following coreBOS philosophy of backward compatibility and "keep things working as they were" the feature is activated by default.