Statuses in Campaign

Hi Folks,

Whenever I create a Marketing plan/Campaign/element I see four statuses by default in status drop down(1.Approved 2.Finished 3.Locked 4.Rejected)

I might not require all these statuses in my current business scenario.May be I need only created,released and approved.Should I remove other statuses or how?

What is Locked?Finished?Rejected?Can I use them?

Regards

Jaya