At low levels, all it takes to drop most characters is one solid hit, and at high levels, damage outpaces healing so significantly the only healing spell capable of doing much good is Heal, so at no point is in-combat healing ever useful except for stabilizing dying allies who can't stabilize on their own, and even that can be accomplished with a Heal check. Plus, cure spells, which can be spontaneously converted into, have a range of touch, so to heal somebody who's been dropped in melee means the cleric will have to wade into the thick of it as well.