"exit" vs. "X-ing" out of a terminal

[Clint Harshaw]

Hi all,

Some time ago, I posted a question about mysterious users that showed up 
  when I would do a "who" at the prompt. I have a question related to 
that issue. Is there any difference in typing "exit" to stop a terminal 
vs. clicking on the "X" in that terminal's window? I wonder if these 
extra users are due to my "X-ing" out of a terminal rather than typing 
"exit" at the prompt.

Is there any harm done by "X-ing" out of the terminal?

Is there a proper way to retrieve those users remaining from a prior 
X-out so that I could "exit" from them? (short of rebooting, I can't 
seem to remove the extraneous users.)

Clint