Greater Auramancy protects an enchantment engine by giving your other enchantments shroud. It also gives shroud to enchanted creatures you control, helping preserve a creature carrying important Auras. For two mana, an enchantment-heavy deck can make many targeted removal spells much less useful against its established board.
Shroud stops your targeting too. Once a creature is enchanted and protected by Auramancy, you normally cannot target it with another Aura spell or an equip ability. Effects that put an Aura onto the battlefield attached without targeting work differently, so the exact wording of the support card matters.
Auramancy does not protect itself through its first ability. A second copy or another appropriate protection effect can change that situation, but one Auramancy leaves opponents a clear target. Untargeted sweepers and sacrifice effects can also get around shroud, so the card is protection against a particular class of interaction rather than a complete shield. Enchantress and enchantment-control decks often get the cleanest benefit because they want to preserve several engines without repeatedly targeting them afterward. Aura decks can use it as well, but should plan attachment order carefully. Establish the pieces that need targeting first, then deploy protection when appropriate. The enchantment is most valuable when protecting a board already doing useful work, not when it leaves you unable to complete your own creature-building sequence.
