Experience shows that a volume of approximately 1.5 gigabytes per month is required for daily use.
Of course this depends on how you use NUNAV.
Currently NUNAV uses a so-called "environment caching". This means that only the environment data of your last destinations is saved. After the maximum capacity of 50MB is exceeded, the environment data of the "least visited destinations" is released for the environment data of new destinations.
In this way, you only load the map material that you really need and can always navigate with the most up-to-date map at the same time.
Due to this "environment caching", the data consumption for shorter or recurring distances (for example, your commute to work) is naturally much lower than if you are driving from Hamburg to Munich today and from Munich to Berlin tomorrow. On these routes, NUNAV then loads more data because more map material is required.