[curt.clifton]

Start date is an actual, not an artificial constraint here. By setting a start date, and viewing Next or Available actions in Context Mode, you aren't reminded of actions that are not yet available for completion. (Similarly for projects, but the relevant filter is Pending vs. Active Projects in Project Mode.)

If you have a start date, but no due date for a task, the due date isn't filled in. But with no dates at all, OF fills in one--the due date.

For example, I have an action "Get Loaned Books Back" with a two-months-from-assigned repeat interval and a start date, but no due date. (I keep a separate list of loaned books in an OmniOutliner document. As an academic at a small school, I'm always loaning books to interested students and colleagues.)