Global variables and Local Map variables.

[palistov]

Global variables will reset each time the script is run. (e.g. every time the player re-enters the map, or loads a saved game.) Using the API for variables will make them retain their value. As an example of how this could be problematic, consider a switch-case structure using a global variable used to run a scary event with the shadow roar, falling dust particles, sanity loss, etc etc. If the player (for some reason) exits the map and re-enters, the event might start over or stop partway through. Could be consequential if some critically important things happen during the event, like a door breaking or an item becoming "pickable".

Edit: Apjjm is still the sensei of everything.