I am working on the Differential Expression Analysis on RNA-Seq Data between tumor sample and normal sample, while my lecturer suggest me better use the raw expression data instead of using FPKM as expression unit , anyone could tell me why ? or what is the advantage for this ? 
In a nutshell, because you'll be able to apply statistical models to your values. When you normalize to FPKM you lose your ability to do so and end up with less robust statistical tests