iirc don't operators sometimes use the Welbeck exit to access trains in the storage tracks for the sherppard line?
I know for me the only place that ever caught my attention was the massive attic above Lawrence Station. You can see it from the north end escalators if I'm not mistaken. I assume the TTC uses it for storage space.
Welbeck is essentially access for the tail track. They can lock trains away for the night and exit through there. Unlike most other emergency exits, Welbeck is more of an employee entrance.
