The Hull is “the main body of a ship or other vessel, including the bottom, sides, and deck of the ship, but not including the masts, superstructure, rigging, engines, and other fittings on the ship”. In Roblox Galaxy, Hull is the armor integrity of a ship that is calculated through materials used, ship class, and armour shape/form.
Advantages of Hull
The Hull is the primary armour and exterior of a ship. Hull is calculated by what class the ship is, what materials are used, and the shape/form of the armour. The Hull (or ship armour) can resist damage from incoming Phasers and any Shield Damaging Turrets.
Disadvantages of Hull
While the Hull is the primary armour of a ship, It's better to retreat when your Shields are down, or before your hull hits critical levels. The Hull takes more damage from incoming Cannons and Hull Damaging Turrets. Unless you're sure you can take on an enemy ship while currently at low Hull and no Shields, it's better to get your health back up before fighting again.
In short, having a ship with strong Hull health can help you survive battles longer. With more disadvantages than advantages, it's better to compensate low ship health with good pvp skills and evasive reflexes to survive longer in combat.