You do not HAVE to use a finisher.
They are used when raising cells commercially. What commonly happens in a commercial setup is the cell starter starts 64 cells or even more. However the bees in the cell starter are queenless and have started these cells from their perspective, to make a replacement queen. It does not take them long to figure out they do not need 64 queen cells and they begin to neglect a lot of them.
So after 24 hours in the starter, the cells are usually moved to a finisher. Finishers are strong hives with a queen set up to simulate a pre-swarming situation, and are commonly given 16 cells, which is a number they are happy to care for to a high standard, as any hive thinking about swarming would.
With queen cell raising, it is important to see things how the bees see it, or, think like a bee, if you like. We have to work with the bees, not force them to do things. So we set things up so the bees just do what comes naturally in that situation.