What is the difference between these lines?
#define DEFAULT_MAX_ACCELERATION { 2000, 2000, 100, 2000 }
#define DEFAULT_ACCELERATION 400 // X, Y, Z and E acceleration for printing moves
#define DEFAULT_MAX_ACCELERATION { 2000, 2000, 100, 2000 }
#define DEFAULT_ACCELERATION 400 // X, Y, Z and E acceleration for printing moves