How they works? Definitions of them and there effectiveness
When the one which equips ally healing affix deals damage, he and his ally (you or your hireling) heals for a % of base HP. For instance, base HP is only your HP points, Flat HP affixes and base character HP. It doesn’t count HP multiplicators such Plagued, Faun’s Gifts, etc. Because of that, ally healing values are pretty low and IMO aren’t worth taking in PVE nor PVP.