Copy slides versus Import slides in Captivate 3

What works better when you want to take a few slides from one Captivate 3 project and put them in a different Captivate 3 project -- Using the

     Copy slide function...

            or the

     Import slides function?

From a about 90-slide presentation, I may take about 20 into a new Captivate 3 project file, probably one at a time, as I need each. I've used the Copy function for a few slides so far, and it seems to be working well, but since this is new to me, I wanted to check with you other Captivate users, to see if you had any insights or warnings about either the Copy function or the Import function.

Thank you!