Joining NCC won't help for your NDA exam but it will be helpful for you in joining Indian army and in SSB interview. If you don't know much about army and SSB interview it is better to join NCC because we can learn many things from NCC. NCC will teach you many things.

The things we can learn from NCC are

1.) discipline

2.)Unity

3.) leadership qualities

4.) Management skills

5.)It will increase your confidence

All these qualities which are important for joining Indian army can be learnt from NCC and punishment given in NCC are useful