Always, but always write it down...it may not flow with what you’ve got, but it could be the start of something new. As was mentioned in the last point, separate the creative from the critical. You can always go back and edit later. You don’t want to lose the momentum of your writing. What is coming through you might not belong with what you are writing, but it may belong in or as another piece. Don’t squelch it, because it might not be back.

This is also the point of always having some means of recording your thoughts, like a journal or recorder. You might not remember that idea later, so write it down. Some writers always have a couple of windows open on the computer: one for the current project and another for random thoughts and ideas.