As a manager, here are my reasons: 1. Biggest one: transfer of knowledge between people is lower bandwidth than going to one person. If I have Jill and Jane do

As a manager, here are my reasons: 1. Biggest one: transfer of knowledge between people is lower bandwidth than going to one person. If I have Jill and Jane doing work function A, I can assign primary responsibility to some sub-parts A1 and A2 to Jill and A3 and A4 to Jane. If I need A2 on Tuesday when Jill is off, sure Jane can do it (and as a manager I should make sure of that) but it would take her more time while her othe things slip. 2. Overhead per employee: I have to do one on ones, regular reviews, and various other per-employee bureaucracy. 3. All team update meetings and other get togethers requiring non-trivial subset of the team get exponentially harder to organize.