With this set up, Galio can deal a significant amount of damage from the get-go. Maxing Resolute Smite first allows powerful AoE damage which means that in 1v1, 1v2 or 2v2 laning scenarios, Galio can provide significant harass. Combine this with CDR from masteries and an early game emphasis on mana regeneration, Galio can deal damage at somewhat of a constant rate.

Bulwark increases its targets Armor and Magic Resist which means you can use it on yourself to increase your ability power and therefore the damage output of your other abilities. However, early game this amounts to a minimal effect while it takes mana to use, which can overall decrease your damage output overtime because you run out of mana for more Resolute Smite. At level one, Bulwark gives you 30 magic resist, you get 15 AP of which only 6 translates to actual damage on Resolute Smite. The 60 mana it costs to give you an additional 6 damage could be used 7 seconds later on another Resolute Smite. This said, the option exists so you need to make a judgement call.