Minimal coverage helmets extend just past the basic safety certification requirements, with less material around your temples and the back of your skull. They're designed primarily for aerodynamics and low weight, making them popular for road racing and time trials where every second counts.
The tradeoff is protection. These helmets offer the least coverage for side and rear impacts compared to other helmet types. If you crash and hit the back or side of your head, there's simply less helmet there to absorb the blow.
Minimal coverage makes the most sense if you're racing or riding fast on smooth roads where aerodynamics matter and crashes tend to be forward-sliding falls. It's not a great choice for mountain biking, gravel riding, or commuting, where crashes are more unpredictable and often involve impacts from multiple directions. For those disciplines, look at extended rear or full coverage options instead.