I believe new cars come with free sat nav updates for 3yrs there after one, as yous say, can purchase database (map) updates as and when they become available, usually twice a year(?)
The infotainment system will function perfectly even if one should choose not to update the sat nav database. The only 'downside' being new roads/roundabouts/junctions etc, etc won't be shown. Not usually a massive negative tbh.
Personally I would update but maybe only every two years.