I actually received a Preservation Notice a few years ago when I worked at a large university. There was a troubled employee in our department, somewhat on the schizophrenic side, and she had been sending bizarre and vaguely threatening emails to the chancellor of the university and to our department head. All of us in our department received the Preservation memo, as the administration was working up a legal case to fire her.

So we were told not to delete or alter any emails between us and this employee. I'm sure they were already collected by IT folks, but I think it was part of the legal activities to show how "proactive" the university was in "eliminating a threat."

She was just a sad, lost soul, rather harmless in my estimation, and a bit delusional, but they went to extraordinary lengths like putting locks on the doors of our building, providing escorts to anyone who wanted them before and after work.... typical bureaucratic overreach and paranoia. Last I heard she had moved way out west, New Mexico I think, and was heard of no more.