A handhold for a difficult, hurried movement
That handle is there to give people something solid to brace against while they operate or pass through an emergency exit. Opening a heavy aircraft door takes leverage, and an evacuation can leave passengers unsteady as they turn, step over a threshold, or move toward a slide or wing. A nearby grip helps them keep their balance instead of grabbing the door, which may be moving or need to stay clear.
Why it is fixed beside the exit
In an emergency, there may be little time for instructions or for someone to help each passenger. A fixed handle is immediately available to a crew member preparing the exit and to passengers making their way out. Its placement makes it useful at the point where people must change direction and commit to climbing or stepping through.
The exact handle and its job vary with the aircraft and exit design; some exits also have handholds along the route outside. But the basic idea is practical: give people a reliable grip where a misstep could slow an evacuation.
