haha
I tend to over crowd my room because it is so small. key is lots of air movement both on top and below canopy. That and be careful when you take the plants out. They gain support from eachother and dont build the strongest stock. Your buds will break the stems when you take them out if you dont stake them or hold them up when you take them out.
That and you need to lollipop bc with that much crowding no light is gonna reach the lower growth
good advice
and would add
if the plants are overcrowded the plants will compete for the light and stretch, the stems/branches become weak and the steams and branches rest on other plants,
the airflow is reduced and end up with a thinner canopy as the light penetration can't reach the lower parts of the plants so an less your plants are very short and you are
doing a sog with 20 plants under a 600 you could reduce you yeild a lot
well space plants are more likely to grow shorter and bushy with more bud sites and less stress and increase yeild if your only growing a few plants under hps imo
sog (over 20 plants) and scog ( 1-2 plants)need a thick canopy to get a better yeild