> There even exist situations (in the case of some positions) where you will be talking to a client of the company you're working for, effectively interviewing with the client, representing the company.

What positions would require you to prove the technical capability of your company at this level?

I've been working for a consultancy for a few years now. I can't recall a time when a client asked me to describe a closure or what I thought of !important. If I'm on a development team, the conversation with clients is generally about the time and effort required to implement something, or the options we have for delivering the functionality. If I'm pulled into a sales meeting, it's usually high-level architectural discussions.