Teaching something will make you a better practitioner of that thing. It is an adjunct to the old adage that true mastery of a subject is the ability to teach it to someone else. The act of educating someone on something forces you to organize your thoughts on that subject. This, in turn, gives you new insights on the subject and/or makes you more efficient at processing the subject. Therefore, there is a lot of value to the teacher in the act of educating.
There is a business value as well. But a lot of managers, however are not comfortable pushing their team members to do so – particularly if they have team members who resist doing it. I have spoken to a number of managers who really have no idea how to break down that resistance. There is obviously the ‘stick’ side of it where it should be a part of a senior person’s job description and if they don’t do it, their review will not be as good as it could be. But the stick side is a pretty weak instrument and it just breeds problems over the long haul. The more important aspect is the carrot side of the discussion.
Look at it this way: no matter how good a coder someone is, their value is intrinsically limited by the amount of code they can physically produce in a certain amount of time. That means that once they reach their personal peak productivity, they are basically plateaued in terms of their career opportunity due to laws of physics and biology (i.e. only so many hours in a day and humans need to sleep). Contrast that with someone who has reached their productivity peak and uses their skills to help make others better. That person is now leveraging their skills through a larger group and enhancing the produtivity of that overall group by passing on lessons and learnings. They are multiplying themselves through that group. That person’s value has not plateaued. This does not mean they are on a ‘management’ track, either – though it can lead there. I have found that engineering organizations that have been successful over time all have a non-management ‘technical leader’ career path for folks who are both strong technically and effective leader/teacher/mentors. Does your organization think like that? It should.
Even if it doesn’t, it is irresponsible of the manager to not at least have a frank conversation about this to their team members. That a team lead does a massive disservice to a team member’s career if they just encourage them to be ‘super techie’. It will fundamentally limit their team members’ value and the value of the team in general.