Best practice is NOT to use a back button unless it is necessary.
If you are building a "wizard" (the user has entered a next/previous flow), a back/previous button could be desirable.
If the site architecture is very deep and has pages buried within pages that take several steps to navigate to, a "breadcrumb trail" may be more useful than a nondescript "back" button.
You have to ask your friend, what problem is the back button trying to solve?
In all usability studies that I have conducted and observed, users will overwhelmingly select the browser back button - even when an alternative back button is provided.
Historically, "Back" buttons were considered good usability because many browser-based applications did not have functional back buttons. In other words, the "Back" button would return the user to some unexpected location or it would throw an error. This led to heavy back button usage, and a lot of misconceptions about back buttons being good usability, when in reality they were a workaround.
In some older products, or products that do intensive db queries, this problem often lives on. For a shiny new product that is architected in such a way that the browser back button works, you should carefully evaluate the need for this extra button - and use it sparingly if at all.