I love to use Heaven's Wrath when I play reg (imo the only dg who should ever really get it anyway). But.. I don't use it every cd. I used to use it in the other lane while i was killing creeps in my lane for double xp.. but ya.. ur teammates dont liek that 
Times to use Heaven's Wrath as Reg:
1. Extra dmg on snipe. I've gotten so many fcking kills from wrath on top of snipe that otherwise wouldn't have been kills.
- Can't do this if you wasted it on creeps for no reason. Good reason to save it.
2. If you're solo in a lane and attacking a tower with a fresh creep wave all attacking you. No xp stolen from anyone, and
minimizes your dmg while allowing you to continue doing more important work - killing the tower.
3. If a lane is abandoned due to you or teammate shopping or capping mid. Great time to use it 
4. To see someone in the fog so you can snipe them. Another thing that has gotten me several kills. "Shit snipe was on cd
and now I can't see them" sucks. Use wrath where you think they are to catch a glimpse and you have a split second to
target them for snipe. AWESOME 
5. To get an assist on a kill. Let's say you can't snipe the guy before he's going to die, or it's already on cd... great time to
wrath just to get a piece of the action and get that assist gold. Try not to steal the kill though as you could miss getting
an assist at all (plus people don't really like kill stealers but who fckin cares? You're reg.. you snipe.. and you steal kills
)