Yesterday while running challenge golgoroth, I ran into several defenders not using the illuminated perk, which I found surprising to say the least, so I'm making a post here to show why its important.
[b]Illuminated is the bottom perk in the far right column that increases the damage buff from weapons of light from 25% to 35%. So if you were doing 100,000 damage per shot to golgoroth without weapons, you would do 125,000 with weapons of light (no illuminated) or 135,000 per shot with illuminated (all other things being equal).[/b]
Weapons of light also stacks with tether or melting point separately (but not both at once because tether overwrites melting point), so the amount of additional damage gained from illuminated is further increased when a tether or melting point is in use.
Not using illuminated or not using weapons at all adds up to a LOT of missed damage over the course of the fight (5 people shooting about 15 sniper rounds per DPS phase). Not using any defender titan is even more missed damage of course.
Note that as a titan with max intellect and the inverse shadow perk on my helm of saint 14, i can EASILY have a bubble for every DPS phase on golgoroth. Inverse shadow probably isn't even necessary. So using the perk that recharges your bubble a bit faster is not necessary at all in this fight, especially if youre using 2 defenders or someone is making orbs for you.
The same goes for the oryx fight, both your blessings titan and your weapons titan should use illuminated at all times. Illuminated also increases the benefit of blessings of light from 35% to 45%. Source : http://www.destinygamewiki.com/wiki/Illuminated
Side note : Melting point gives a bigger damage buff than tether. Both melting point and tether stack with weapons when used separately, but a tether cast on top of a melting point will cancel the melting point debuff and overwrite it with a tether. Source/video proof : https://www.youtube.com/watch?v=lmDiPPDTdfg (this is a video by datto, not my video).
Side note 2 : Bastion is useless in the golgoroth fight if youre doing the one bubble strat. Use gift of the void instead. Its pretty easy to kill a cursed thrall near the bubble after jumping out of the pit to make 3 extra orbs.
Comment if this helped you.