Can someone tell me how "Leave all attributes in" and "move all attributes into the new composition" are different from each other? What are the differences between the two options and how do you know which to choose for different occasions?
I assume that you've already read the description of the options in the
"Precompose layers" section of After Effects Help on the Web.
I did a search using the Adobe Community Help beta, and found a lot of tutorials and threads that mention these options. You could peruse them and get a good sense of the different uses that people are making of each of these options: