CPT = Curriculum Practical Training, and OPT = Optional Practical Training.
If I remember right (it's been a long time since I graduated), you could apply for CPT before you graduated for something like say a summer internship, while you applied for the OPT, which is for a maximum of one year usually used after course requirements were complete.
However, I agree with your suggestion, as (again, if I remember right), an individual can only get a maximum of one year of OPT throughout his lifetime.
That being said, there are tax benefits to extending your F1 status (i.e., being on the OPT), since as an F1 holder, you are exempt from SS/medicare taxes.
K