As said, depends on grow space and veg time. Unless working in large area (or with small plants) a square grid configuration is probably most efficient, so going from 6 to 9 plants would nock a week or two off your veg time.
Something I'm just learning is that too much vegetative growth can have a severe effect on yield and quality. Plants produce fluffy bud as a defense against mold growth. This can be due to temps being too high or too low but also because the canopy is too thick and airflow is lessened. So flip early or do some strategic pruning. I suspect that if there's any truth to defoliation it's in regards to airflow through the canopy, though there's obviously a big difference between pruning and heavy defoliation.
Some peeps think LEDs are a joke, but plants are crazy about COB light. I grow crazy big bushes in 3 weeks and have had constricted canopies even after trimming branches and lollypopping. I'm talking about all the leaves going vertical because they're pushed up against themselves. In such a situation fluffy bud below the canopy is basically a guarantee, and no amount of light penetration is going to fix that.