I always wondered why people don't start their plant in pot they on growing in. Unless the plant is root bound the whole transporting seems pointless . Just unnecessary stress on the plant
The reason for transplanting is to allow the plant to fill up the smaller pot before moving to the larger pot. This helps promote a stronger and healthier root system. Alot of people do use a single pot but most prefer to start small and work up.
If you're growing regs but not breeding then its sometimes better to start them off in small pots until they show sex so you're not wasting more soil on the males. Its just a matter of choice, some of my friends start them in big pots but I like to transplant them into bigger pots when they need it. Might give them the stress or a transplant or two but I like potting them into fresh soil
Easier to properly water a baby sprout in a small pot -- in a large pot the soil could still be damp but the sprout's roots aren't yet deep enough to reach it. I agree that there is no need to transplant multiple times. I plant germed seeds into 4" pots, after they are established I go from there straight to their final 5-gallon buckets.