Migration Advantages and Disadvantages

Dear Sdns,

We UpgradeBw 3.5 to BI 7.0.. Now We are in plan to do migration.. Before doing migration I wanna know what are the major and minor advantages and disadvantages. Also what are the precautions to be taken.. Can anyone guide by Step-by-Step..

Kindly Advice me how to do the migration with precautions....

Answering getz appreciated.

Warm Regards,

Aluri