The first one is used in situations where there is some distance between the speakers, the second when they are (much) more familiar. It used to be fairly unheard of to hear a German 'subordinate' use 'du' to their superior, whereas in English it would be impossible to even express the difference.
So in Germany workplace relationships tend to have a sense of distance between the various strata. Even if you didn't want to change your personality the simple fact that you'd address your superior in this way would make you behave differently (and so you would show a more deferential personality), because associated with that distance are a whole pile of other personal traits.
It's not as strict as it used to be, but the difference is definitely still there.