[Suicide Junkie]

In Se4, building one turn's worth at least allows you to quickly optimize your production rate. (Although building more usually results in 5 units in 4 turns, rather than one per turn for example)

In SE5, one turn's worth provides no such advantage.
One turn's worth means that you don't know how many you really want.


If you were to put one on repeat build, then you'd end up with 30 fighters and 30 carriers.

What you want in the example, is a bunch of carriers and 30 fighters to fill each of them.
Building 30 fighters (perhaps 10 bombers, 10 interceptors, and 10 dogfighters), then one carrier, and hitting repeat build, means that each time you finish a carrier, you have built exactly what you need (30 fighters) to fill it and send it into combat right away.

When you know what you want to end up with, one turn's worth is irrelevant. You get what you want as fast as it can be produced.
And if you are really stuck on it, you can do the "build 1, repeat" thing.