Are you familiar with the five zones of cardio?

A relaxed swim in Zone 2 cardio is a continuous, steady-paced aerobic workout where your heart rate sits at roughly 60% to 70% of your MHR, allowing you to maintain a steady breathing rhythm. — dpa

Is it necessary to go all out during your cardiovascular workouts to reap the maximum health benefits?

My younger self would have said yes (the adrenaline rush felt good), but my current self would disagree because really, slow and steady can still win the race and make the lifelong journey with fitness more fulfilling.