There are two different kinds of finisher. One is the 15% protein finisher, You can use that for chickens that will be layers, not meat birds. You can feed that finsher from week 13 until you switch to Layer. I know that is not what you are talking about but I wanted to mention that there can be a difference to hopefully avoid confusion.
The Finisher I think you are talking about is a 19% protein product. It is intended to give the meat birds a diet high enough in protein to keep them growing optimally without getting them to grow so fast they have premature medical problems. Those broilers can outgrow their skeletons they grow so fast. The 16% Grower is not high enough in protein content for optimum growth. Plenty of people use different products and strategies, including feeding even higher protein levels. The 19% Finisher is an efficient feed, but you need to look at how to feed it too. Some strategies require restricting access.