What's up with Version Names in Apple Aperture?

Here is one thing that puzzles me in Apple's Aperture: It provides a field "Version Name" for each photo. This is the one field that can be populated automatically with some pattern, for example date and an index number. This is also the only field that can be used as the master file name.
But it is also the field that is used as caption for online publishing, books etc. So what does Aperture want me to use the version name for: a descriptive caption or a auto generated index code/number?