Used to send a log file to the developer!
Collects the log from the system.
It will be zipped, saved to the SD-Card and send with an application of your choise like GMail, etc.. !
On Android 4.1 (Jelly Bean) this log file only collects the log written from the app itself, not the complete log from the system!
This is a new security from Google on Jelly Bean.
Apps can only read there own logs.