[HDPhoenix]

3 port banshees with cloak is unbelievably strong because if you're not prepared for 6 banshees at once, you're essentially dead.

The thing is, to get 6 banshees with 3 ports with tech labs, requires a massive amount of gas = no offensive pressure other than pure marines or delayed 3 port banshees = plenty of time to scout it

As a zerg, you can throw up a hydra den really fast and pump out more hydras and queens to effectively stop 3 port banshees if you scout it early enough. Similarly, you can deflect it as the other races too. If the 'cheese' fails, they would be severely behind because banshees are not very good front-line units.

TL: DR

Short form - CHEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEESE!