Each data plan you buy is valid for a specific region/country for a specific number of days. When buying a plan for a region/country for a particular period of time, you can start and stop using the plan as many times as you like. The only imit is the number of days and the amount of the megabytes.
When you are in a country/region that is not included in your current plan, MobileXY will be registered on a local network but you won’t be able to use data. In this case, the balance will remain the same.