<aside> đź’ˇ Because of the new "frames" interface that's currently in beta, this workflow will probably become irrelevant soon.
</aside>
One of the main reasons to track rolls of film in Cassette Nest is to know what days you started and finished a given roll. Getting more granular, the main reason to use journal entries is to be able to track what day you shot any frame of any of those rolls.
Journal entries are freeform by design. You can track as much or as little as you want. The only restriction is that journal entries can be entered only once per day, per roll. The idea is to end up with a table of contents of frames for your roll.
The freeform nature of journal entries is all about the Markdown field.
So freeform.
You're free to use this the way your would another journaling program…
Just text.
Or keep track of information about individual frames…