Re: flip flops types?
Hello, Abhineet22.
Well, about "Why are there more than just one Flip Flop", I think is for convenience.
For example, if you need a circuit where you want the output to be the same as the input, is better to use a D-Flip Flop, because you'll need less connections to make compared to a J-K FF where to acomplish the same you'll need to connect the input directly to the J pin, and through an inverter to the K pin (so you save space in your circuit and money, eliminating this "inverter", when using the D-Flip Flop).
Once in the university a proffesor told my class:
"D-Flip Flops use less transistors, so they are useful in integrated circuits. While JK FF are more versatile, so they are better to use in circuits with discrete elements".
Hope this helps.
Regards. 8)