I agree that it can be very successful to use a series of growout tanks for your fish, with some experience in properly setting up the tanks.
I do not agree that it is good advice to give.
Far too many times I see someone use a growout tank, with the initial intent to upgrade later, only to find a 12" Oscar in a 20 long.
I think the intent to buy a larger tank later is a trap for horrible living conditions to the non-motivated enthusiast.
Just my 2 cents.