My book says it's need a format everytime i plug it

WD External Drives External Drives for PC
2

Hi, could be a data corruption problem, you need to be sure to always safely eject the hard drive before disconnecting the USB cable. You can try backing up all of your files and then formatting the my book. 

http://wdc.custhelp.com/app/answers/detail/a_id/3865

http://wdc.custhelp.com/app/answers/detail/a_id/5316