Especially when you look beyond the hubris of the word "career" and consider that a very important part of "building a career" is growing your skills, experience & knowledge. That's something both employee and employer should want.
In my experience, when you help people with their long term goals, even if it's not their core job, you get a much more motivated team member.
I'm a big fan of what Reid Hoffman advocates for in the Alliance; work is a two way relationship and if we treat it that way, and are honest about it, we can all benefit more.