Lets say i spend 12 mana on some creature (casting cost and enchantements). I attacked first and after its activation, i cast sanctuary. Now my heavy creature is safe, my oponent need to target something else.
or
Lets say, i have a creature with 1 life left. I will have initiative next round. I will sanctuary him and use him next round as a first creature.
Also, as more cards will came into academy, more cool interactions and combos will be possible