For engineers/developers, mentoring is not necessarily having a seasoned person training someone with no experience. Everyone on the team has a different background and experience. We ran into an issue the other day where we identified a developer misunderstanding how a certain kind of technology is supposed to be used. This developer is outstanding on many levels, super focused and a great asset. English is also not their native language. Try describing a concept over Skype with paint.exe. It is much easier to put it on a white board so everyone can see how their piece fits into the larger picture. Having everyone in the same location brings synergy you can’t achieve in remote locations and timezones especially if you are a startup.