Many people focus on light, soil, nutrients, water, and shaping/pruning ... while completely ignoring air!

My first indoor garden had a massive tube connected to the outdoors that acted as the intake to the two rooms I built inside my garage. On the opposite side of the rooms, I had a squirrel fan (slightly oversized) exhausing air into the garage.

Fresh air is important, and you want lots of it. There are some strains that won't mold, even with tight/dense buds. There are other strains that are prone to mold. Having a high concentration of CO2 will also help with keeping mold issues to a minimum, or even non-existent.