When to use HE ammunition?

ARGO: HE rounds tend to drive me nuts, half the time I can't tell if they have done anything cause the enemy doesn't loose HP. Then I will hit them and do 20-25% damamge. How can you tell if you messed up a tank with it? All I know is that for me at least itHE tends to be fickle. Either that or I don't hit the right spot. I have been hit and all mys systems go bye bye and my crew reads off a never ending list of damages.
Oh yeah, I kept hearing how Tigers can't take HE rounds, BULLCRAP! I hit one 8 times and all I got was blown up. If a 107mm can't hurt a Tiger with an HE round, then I am sticking to AP.