When to use Static Lists vs. Dynamic Lists
When building a new list you must choose a list type, either static or dynamic.
Dynamic is the default and will be used in nearly all cases. A dynamic list will re-run the entry criteria periodically (based on the auto-refresh settings) and dynamically add/remove contacts from the list in FrontSpin (e.g. some new leads came in that match the criteria, so they are added to the list automatically... or some leads were disqualified and no longer match the criteria, so they are removed from the list automatically).
The fastest auto-refresh period is 15 minutes.
The case for using static lists would be any time you don't want the entry criteria to be re-run. A prime example would be for a playbooks where the entry criteria has a time condition (e.g. last activity date < 90 days ago). Let's take this playbook as the example...
Which is powered by this Salesforce report...
If the list type were dynamic, the entry criteria would be re-run and contacts in this list would automatically be removed after getting the intro email (because the last activity date would now be today's data). In this case, the contacts would never move through the playbook as intended. Because of that time condition, it would be best instead to set this as a static list, which will never re-run the entry criteria and will therefore allow the contacts to move all the way through the playbook as intended.