The Regeneration Field is a very useful armor ability on most maps. It requires a short animation to activate during which you are helpless but once activated, anybody who stands in the green field will have their shields quickly regenerated provided they are not being shot at.
It clearly has uses even just on your own. In a firefight, if you retreat around a corner and activate the field, you can recharge your shields and start the fight anew. Not only does this provide the bonus of recharging your shields, it can also through off an opponent who is expecting a shieldless enemy.
When used with teammates, the effects are even more profound. Rather than having a teammate retreat for 5 seconds to recharge their shields, they can recharge almost instantly, allowing them to get right back in the fight. This keeps the teams damage output at a much higher rate, allowing the team to score a crucial kill which can dramatically tip the scales in their favor.
The field is most useful in areas with lots of corners since it is most useful when you are not being hit and when your opponent doesn't know you are using it. Most maps have areas like that so making good use of this armor ability is just a matter of finding one of these spots.
