Applications for a watchman clock system:

Condominium associations:  Proof that the staff is checking the doors, gates, pools, golf course, boat docks.
Retirement centers and hotels: Provides proof that the staf is checking the gates, doors, recreation rooms, casino, etc.
Pool and other contractors:  Provide printed proof, and computer records during an audit, that the facility was visited by your staff. 

Basic mechanical clocks such as the Detex Newman, Detex Guardsman, and Amano PR600 show that "someone" was at that station (by number only) at approximately the correct time.
Computerized systems, such as the GuardQuest or Detex ProxiPen with TopGuard software, provide reports that include the security guard (or contractor's) actual name or ID, exactly what time they were there, the location - by NAME, and optionally, if an "Incident" happened. 
An Incident is typically a preset general button that is read for things such as:
Door unlocked      Suspicious person     Unauthorized entry     Window open     Checked pool
And on and on.  Reports can be created in the software, you can go back to any station, any event, any guard and build custom reports either in the basic software that is provided, or by exporting the Excel file and making your own.