Well, the basic idea for coaching a brand-new employee is that you hired a perfectly smart person for the job, but your company has a strong coding culture with a particular style that the new engineer isn't familiar with. So it's a big part of on-boarding to not only teach this smart engineer the crazy weirdnesses of your system, but also teach them (what they will perceive as) the oddities of your corporate coding style.

It can be good to do this outside of the public eye, so the initial cycle of "wtf, why is this considered standard" followed by "well, it's not so much that this is the best way, but it's more likely that we'll be able to understand each other's code if we all do it one way" can be done in private.

Once the engineer is well-versed in the system, they are unleashed to quietly subvert it, if that is their will :-)