1. A flip-flop is essentially a 1-bit memory unit. Such memory units are highly useful in digital computers to store a binary number or to keep the information of previous counts and additions until these are needed. Memory circuits can be built using many flip-flops.
2. Flip-flops are the fundamental building block for sequential logic circuit. 'Sequential' means that the output of each FF feeds the input of the next FF to decide its action.
3. Flip-flop (D flip flop) can be used as frequency divider.
4. Flip-flop can be used as shift and storage register.
5. Flip-flop can be used as counters.
6. Flip-flop can be used to generate a variety of one rectangular pulse (such as monostable output) of any width.