What is "playing too long"? How much is too long?
How long is "rest for a few minutes"?
What is the purpose of this feature? Player benefits? Account maintenance?

What is "playing too long"? How much is too long?
How long is "rest for a few minutes"?
What is the purpose of this feature? Player benefits? Account maintenance?

The Personal Break was introduced in the May 2013 patch. According to this thread on the forums, a break will occur after eight hours of continuous play; you'll need to close the app for a few minutes before you can play again. This was apparently introduced to prevent players from staying online continuously and avoiding attacks.
Update: the new patch 12/10/15 has shortened the amount of time you can play consecutively to 3 hours after which you must take a personal break.
Here's a response from staff on the forum when the feature was introduced: http://forum.supercell.net/showthread.php/54871-The-Update-Stinks-Raging-Thread?p=467710&viewfull=1#post467710
– bobpaul Aug 13 '15 at 15:43Happened again, now I timed it. It takes exactly 5 minutes before you can play again.
Note: Changing devices does not fool the system, no need to try it.