High templars are expensive, gas requiring floaters who can cast the most devastating spell in the game: Psionic Storm. Train a couple of these Adun sorcerers and upgrade Psi Storm immediately. Send a templar or two with your attack force and cast psi storms while your spearhead units are engaged. Defend a base using a few of these templars and some photon cannons.

PSIONIC STORM
75 energy and 3 by 3 matrix, this spell is the best in Starcraft. How do you win a game, eliminate your enemy's units to defeat his bases and achieve you goal and psi storm can do the job. Do not target the same unit with a psi storm, instead, stack them to deal multiple damage.

HALLUCINATION
125 energy, this is not so much of use but can be effective if used properly. Hallucinate best your spearhead units and attack with them then your real units to buy time for efficient positioning. Hallucinate also to scout the map and increase surivability of shuttles to drop reavers etc.