A local rule is a change or addition to the standard Rules of Golf that your league's committee adopts for its course or competition. The app does not record which local rules your league uses, so ask the organizer.
Who decides?
The committee, which in most leagues is the commissioner or the organizers. The governing bodies publish a catalogue of model local rules that a committee can choose from. The committee decides which to adopt, for all play or for particular holes.
What kinds of things do local rules cover?
Typical examples are a dropping zone for a penalty area, a rule that gives lateral relief on the opposite side of a red penalty area, limits on relief for a ball embedded outside the fairway, and Model Local Rule E-5, an alternative to stroke and distance for a lost ball or a ball out of bounds. See Out of bounds.
Should the committee tell me?
Yes. When a committee removes or changes a local rule for a competition, it should make sure all players know before play begins. Check the scorecard, the pro shop, or ask your organizer.
What does the app know?
Nothing about your league's local rules. If you ask Caddie a rules question, it gives you the standard rule and tells you to check with your organizer for any local rule.
The model local rules are in Committee Procedures, Section 8.
Local rules
Your league's committee may have local rules that change this. Ask the organizer which ones your league uses.