Assuming this is a PADI course (based on your profile) you didn’t mention that it’s not only doff & don, but actually an equipment exchange with a buddy while sharing a single second stage. Some respondents may not have been aware of this.
I still don't understand the learning value of this event. Why in gods name would you ever swap gear with your buddy during a dive?
I can understand removal and replacement to untangle, modify configuration, solve a problem etc, but just to swap gear with a buddy?
There is no educational value in this task(as I refuse to call it a skill), and I don't see why it is still around...it's as stupid as fin pivots.