Lane bully, skirmishing, and front-line tankiness.
Durability and crowd control
After immobilizing an enemy champion gain defenses and later deal a burst of adaptive damage around you.
Whenever you gain a shield, your next basic attack against a champion deals bonus adaptive damage.
After 10 minutes gain 8 Armor and 8 Magic Resist and increase your total Armor and Magic Resist by 5%.
Gain permanent health when enemy minions or monsters die near you.
Empowered abilities and resource manipulation
Hitting enemy champions with a spell grants maximum mana.
After reaching 250 mana, Manaflow Band restores 1% of your missing mana every 5 seconds.
Gain 10% CDR when you reach level 10. Excess CDR becomes AP or AD, Adaptive.
+5 AD or 9 AP
+8 Magic Resist
Aftershock is the successor to Courage of the Colossus, but rather than granting a shield it does damage and give a ton of Armor and Magic Resist. Galio loves Magic Resist
Shield Bash synergizes well with Galio's [W] shield, granting a bit of extra resists as well as offensive power.
The extra resists from Conditioning empower your ability to absorb a ton of damage in the mid game with [W] and also grant additional damage reduction on your [R].
Overgrowth on Galio makes you a late game monster, empowering your health pool to be a huge frontline tank that dishes out a lot of damage.
Galio's abilities have relative high mana costs and be needs to spam to keep up with wave pushes. Manaflow Band will give you the needed mana sustain to shove and roam.
Entering the mid-game, Multiple successful taunts from [W] will make or break your teamfights and CDR is what enables that.