While I’m sure security is the reason for this in some buildings, in my office building and other buildings I’ve been in, I’m pretty sure the reason is to save energy by moving people more efficiently.
In my building, they spent a lot of money switching from the regular up/down button, floor buttons in the elevator system to the current system where you choose your floor on a screen outside of the elevator and it tells you where to go. You can choose any floor in your elevator bank from any other floor, so it’s definitely not security. They wouldn’t spend all that money for no reason, so we all suspect that it helped them get green certification or something like that.
I’ve been in other buildings where only the ground floor makes you choose a floor first. But, once you’re on another floor, you go with the old system – press up or down then choose the floor inside the elevator. Maybe they get partial credit for that.
I don’t know why it’s more efficient or greener to do it that way, but I can’t think of any other reason why my building would change things over.
The real downside to the system is that now I find when I’m in a regular building, I often get into the elevator and just wait, forgetting to press the floor I want to go to. More than once, I’ve gotten in, the doors close, and I just wait. I finally notice I’m not moving (or the doors reopen to let others in) and I remember to press the floor button.