Title says it all. Sometimes you forget if that last water shrine was finished, or if you still have a few turns left. Also there's plent of room on the screen for it. Alternatively, in the Tool Tip for the spell, calculate the mana shard bonus directly in the tool tip text.
eg: Does 15 Damage + 6 (2 per fire mana shard)
That way you can make a better decision as to whether to use the POWER attack, or flaming hands!