When am I supposed to use Total Eclipse?

[Furious]

Since this skill does not have added enmity, when am I supposed to use this? Is there a certain number of enemies where this becomes the optimal ability to use?

It just seems weird to me that they wouldn't replace flash with this, flash is such a boring skill besides the blind effect.

Flash is an amazing skill BECAUSE of the blind effect. Having both flash and total eclipse is amazing. Flash for very high aoe threat and defense, then spam eclipse for damage on aoe pulls. It doesn't have added enmity but flash has a lot, and if you're in shield oath it multiplies your enmity anyway.

The simple answer would be "as much as you can on aoe pulls without losing threat, running out of tp for following pulls, or dying".