The card Healing Salve is considered the weakest of the five boons in Alpha. This was an ill omen for white, as many of its devotees feel that it has consistently been given short shrift of all the colors.
It is very weak, for example, compared to Lightning Bolt. From the first turn, aiming Lightning Bolt at your opponent leaves you with about a 17.6% life lead over him or her; whereas a first turn Healing Salve targeting yourself leaves you with only a 15% life lead, and the opponent is no closer to death.
Healing Salve appeared in all core sets until Eighth Edition, but has only been reprinted once (in Duel Decks: Divine vs. Demonic) since then. For Dominaria, it was finally replaced by the strictly better Healing Grace.
Healing Salve was revisited in Planar Chaos as the green spell Healing Leaves, which is functionally identical to the original in all ways but the casting cost: instead of . Since life gain/damage prevention is less common in green than in white, Healing Leaves is not as grossly underpowered as Healing Salve, relatively speaking.