If you copy a variable from a screen and try to create a client variable just by pasting it is not created.
This copy paste mechanism is very handy in the platform, and it would be very helpful to have it.

Real examples:
1.I have a screen in traditional I'm converting to reactive.
This screen has 15 session variables, I'm able to copy them and paste them from one module to the other and paste them as variables but not as client variable. In reality SS only allows us to paste cliente variables to client variables folder.