Medium size is little more than a staging area, a middle ground, it has some impact on maximal size but with a little know how it matters not so much what size your pots are and more about how often you can visit them on any given day.
Someone who has a very busy life and only has a small windows of time to spend with their plants might use bigger pots that require less frequent visits allowing for watering every 2 or 3 days.
Someone who grows full time and can spend all day or night attending plants can devote much more time, therefore can feed several times a day in much smaller pots but still procure the same amount of developmental growth. (Yield)
It really comes down to what fits your routine and free time. Bigger pot does generally coincide with bigger plants, but its complex and not as simple as one size fits all.
Having a nice balance between both is generally recommended but equally you can grow with a 100 gallon pot or 1 gallon pot. The medium is the middle ground, the staging area, how you use it is up to you and how well you can keep everything flowing, flowing is growing, bigger pots just mean the flow lasts longer before you need to come and get her up and running again. Don't want a small pot running dry after 5 hours of sunlight, then sitting doing nothing for the next 7.
Gluck with growth.