If you dont have strong hairloss genetics, I dont know that you will ever lose as much had you not taken it.
Someone that is very hairloss sensitive may still go to a NW6, but say you have someone that would be a NW4 at 60, he may never progress past a NW3.
Plus, if you get enough age on fin, it allows you to look good at a much lower density.
There are a lot of advantages getting an extra 15 years or more with good hair.