Those abilities you can use Interject on ALSO stop the enemy completely like a Stun would, and never depreciates either so if it gets a second chance to use said skill Interject will still work the same while Stun might still be in a depreciated, or even immune, state.

For the most part it hasn't been used for bosses, but there are certain trash mobs with big AoE hits that you will want to use it on, more so if you have two of the same mob. Those things will HURT if allowed to cast them together.