What is the importance of implementing a Fault Tolerance System? Are there limitations?

Fault-tolerant systems are systems designed around the concepts of fault tolerance. In real sense, they must be able to continue working to a level of satisfaction in the presence of faults.

or 

Fault tolerance is the property that enables a system to continue operating properly in the event of the failure of (or one or more faults within) some of its components.

Limitation

1. No single point of failure – If a system experiences a failure, it must continue to operate without interruption during the repair process.
2. System must  have enough storage to over come from FT .
3. All  the storage must be in share storage mode.