Regenerating health is important to keep you in the game, although you have a fair amount of health. If the other team has even a decent defense, your team will likely be knocked out left and right. As players are limited to how many times they can be knocked out before they die, it is important that they get the least knockouts possible. Even having one person dead and unable to play can drastically effect a team's ability to function well, so health regeneration is incredibly important.
Although not necessary, the easiest way to regenerate health is to hide behind one's goalie or otherwise hide while awaiting your auto heal to begin. Autoheal starts in a few seconds, but the amount of time can even be cut in half if the skill Bruce Campbell is active. The amount of health gained from autoheal can also be increased if the skill Quick Mender is used.