It's not hard to get dmg to attacker well over 1k, and with some really absurd gear you can get up to 2-3k (demon skin). W/ 10-15% lifesteal this means that any time you are hit you gain 5-10% of your life back. This fills a gap that the regen + 35% cap doesn't, namely large amounts of enemies pounding you for small amounts of damage.
Only issue I see with this is that I don't know if dmg to attacker and lifesteal work together like that. Any thoughts on this?