Part of the point of care plans in nursing school (and I don't know a soul who liked them!) is to get you thinking about what the patient needs, based on his medical diagnoses, your physical assessment, and whatever treatments have been ordered. You list these needs, you list interventions you can perform to meet those needs, and you evaluate whether they worked or not.
For nursing school, the care plan is usually a one-time thing, set to help you think about your patient(s) for clinical and how you will best take care of them for those several hours. In nursing-world, you do the same thing...only most of it takes place in your head, and it takes place many many times over in the course of a shift, and most of it never gets written down.
On my floor, there is a preprinted plan of care. Nursing diagnoses, interventions, and desired outcomes are preprinted, and we check them off as applicable. It has to be opened on admit and the problems closed as appropriate. Once the problem no longer applies, there is a space for us to sign and date indicating we've 'closed' that problem. There are also blank spaces for us to use in case none of the preprinted stuff applies to a particular problem. I work nights and when I do chart audits, I take a look at the careplan to see if anything needs to be closed or opened. Other than that...I will be honest, I don't think anyone actually looks at them. But they are a requirement.