As long as you are using formula, it's because formula due to it's nature can contain a very harmful strain of bacteria that can get inside scratches and cracks on plastic or glass bottles. But you basically only use formula for a year so after you are done with it, you shouldn't have to anymore.
I stopped at 6 months started only washing them with soap but i would sterilize once a week before 6 months i would sterilize daily
As long as you are using formula, it's because formula due to it's nature can contain a very harmful strain of bacteria that can get inside scratches and cracks on plastic or glass bottles. But you basically only use formula for a year so after you are done with it, you shouldn't have to anymore.