MB Invisibility is used for 5 reasons:
1. It allows you to armour through a projectile and successfully enter the invisible state, this will help to start your zoning, and almost always puts the opponent in a panic state.
2. Once you MB through a projectile into invisibility, you DO NOT TAKE ANY DAMAGE on hit from a projectile that might hit you during a trade as you try to get some force balls on the go, this also works for things such as not taking the initial JIP damage from a JIP combo, or the first hit of someones X-Ray, which in most cases, does the biggest damage as part of the X-Ray, i.e, Kotal Kahns X-Ray ends up at 25%. This is also the same for his regular stealth. You will however take the block damage from a projectile if you block.
You can actually attempt to get regular invisibility out in a projectile trade war, as you will take no damage on start up of the invisibility. I will show this in a video on Sunday.
3. It allows you to counter string gaps and fully punish instead of back dashing or blocking them, same for single hitting armoured wake up attacks. For example, some opponents have safe armoured single hitting wake up attacks, like Sub Zero's Hammer, if you see the hammer and block it, yes you could punish with an elbow dash but the MB invisibility will allow for a full combo punish, and yes, you can use MB claw to counter string gaps, but if your MB Claw is blocked, you are full punishable. Invisibility will still allow you to be wrong and block on a confirm.
4. It allows some strings that would be unsafe on block to be cancelled and made safe, such as 212.
5. It's kinda cool.