Mighty Vision has a few different effects, all related to letting you see information that would otherwise be hidden:
- show enemy hit points.
- draw a line over enemies, to locate them without a line of sight.
- show invisible enemies.
- uncover boobytraps.
The general effect of all this is to let you die less and kill your enemies more. You'll know better when to retreat (because you're fighting someone stronger than you) and when to press the attack (because they're about to die). It's a small but significant tactical advantage; I find it very helpful. But I've noticed that beginning players rarely use it. Perhaps it gives more information than they can use effectively. Perhaps they just don't think of it while they're busy with everything else (if this is your problem, try setting it on automatic (Alt+A) so that it'll be used whenever it's ready). Or perhaps they just don't realise the value of the information - it's easy to underestimate abilities that don't give a direct material advantage.
The original design for Mighty Vision was quite different; your avatar would be stuck still (as with Guided Bomb) while you move your view around (as with Teleport) to look at stuff. This was pretty weak, because it was rare that any advantage you could get would be worth using up your BLUE energy and spending that time vulnerable and not doing anything. Now you can use Teleport (or just die) if you want to have a peek around like that, and as a bonus you can get straight there if you see somewhere useful to be.