To (I think) clarify some of the answers on this part, only insofar as your Quality level increases the level of your final Delve Chest once you beat the Boss room. Quality level 10 increases your final Delve Chest by an extra 3 (+4 total). A higher Delve Chest means a greater number of random loot drops (1 per level), which are then multiplied by your Room Multiplier.
Here’s an explanation of Delve Chest drops from Mithran (somewhat long-ish):
and a neat little table of drop values from Ashesekayi:
Hope that helps 
