From Liquipedia Starcraft 2 Wiki
Chitinous Plating can be a very useful upgrade for a Zerg player in mid-game. If you're building Ultralisks, you probably have access to the resources needed to research this upgrade. If the Zerg player has not constructed an Evolution Chamber, or neglected to upgrade ground units, Chitinous Plating can be an effective buffer for the Ultralisk, allowing it to easily match hordes of units with fast-but-weak attacks like Marines and Zealots.
- Adds +2 armor to the Ultralisk rather than +1 armor to all ground units with Ground Carapace upgrades.
- Researches faster than any level of Ground Carapace, so it can be researched in a pinch, or to buff an existing Ultralisk force.
- Allows a fully-upgraded Ultralisk to carry 6 armor rating, a rating equal to the fully-upgraded Battlecruiser and more than any other unit in the game, excluding the Larva and its Cocoon.
Extreme care must be used in picking counter-units to combat this Ultralisk, as many weapons do very little damage per shot.