What is Role of finite element analysis in computer aided design?

Finite Element Analysis (FEA) helps determine if a part will fail in any way when it is used. This allows you to change the design of the part in CAD so that it won't fail once produced.

For example: If you wanted to make a bike frame, you could create a model of it in CAD and then run FEA. In FEA, you would specify the forces the bike would experience (weight of the rider, the force from the wheels, breaks, pedals, etc). FEA would then reveal where some of the failure points could occur. With that information, you can reinforce the bike in at those potential failure points.