the reason u should start with a small container, is it is easier to maintain, especially when it comes to watering. The #1 killer of MJ plants by newbies is overwatering. With a small pot, u water until it runs through, & then u don't water again until the container is light; u quickly learn how "hefting" or watering by weight is the easiest method to know when ur plants actually needs watering. small containers & specifically the 16 oz party cups r so popular for this reason, as well as they r easy to move around, u can easily fit many into small areas, & r easy to remove for transplant. And finally ur not wasting or watering a large amount of soil for a seedling & it helps to plant ur seedling in a fresh pot of soil, that either hasn't had it's supplied nutrients partially depleted, nor has the added weeks of potential adding of nutrients that increases the chances of salt buildup. So u see there r many reasons why most growers start with small pots.