What is Litchi ! is it recommend by DJI to use with P4?

3rd party app. If you have a crash and DJI determines that a 3rd party app caused it, no warranty.

Litchi is more extended version of DJI Go app. It has some advantages - for instance you can use VR glasses which will block sunlight when you are flying. Litchi and other Apps ( Dream Flights http://www.dreamflights.pro/fly.html) are very cool if you want to try FPV. But, yes, be carefull - there is no warranty if the App will cause crash or other problem.  

Using it and having a crash and losing the aircraft may be a warranty issue.
If the aircraft is sent in and determined a aircraft malfunction happened and had nothing to do with the app then it may be a warranty repair as the flight data recorder could be analyzed verses a lost aircraft and DJI flight records wouldn't register.

Thanks for the replies guys. If there is no warranty i will not use that 3rd party apps.