This has been a great (unpublished?) benefit that I've used many times during the years. Yesterday I was told at CPH that this is no longer allowed, with a memo having been sent out 3 weeks ago. Apparently you're only allowed to stand-by if your booking class is C, which seems to be a moot point as you're then anyway already able to change to any flight with available seats.

To me this is a great degradation, being able to catch an earlier flight on standby when work ends early has helped many times. For me personally this means I can no longer justify buying a Plus-ticket to my employer, as it has no benefit anymore except that there is no change fee close to departure (but you still have to pay the fare difference, which can be pretty hefty and something you may not have time to do at the airport).