Pot (container) size

From your experiences, what exactly happens when you grow a plant in, let's say, a 200mL container? For Americans I think that's 6.??? ounces, at least 6.5. I'm just curious because I hated putting soil
in all of my cups for seeds and I'd HATE to have to mess around again.

ps> these seeds i'm only growing to get more seeds so yield doesn't matter, it's wether i
get more seeds out of them or not if i decide not to transplant