Well, as the name implies, it acts like an escalator, it is a technique to bring you up quickly when in the middle of a fall.
For this case, we will be using the wall as an example, it most likely can be used on titans as a killing move too, but I haven't tested it out yet.
This happens in the Colossal Titan map. After you fall down from the wall, perhaps from a Gas Blast, an accident, etc…
You would want to reach the top fast with just a few shots of your hooks, instead of hooking and hooking and hooking and hooking and hooking and….. (you get the point

This is where Escalator Reel comes in, basically with this, you can get up the wall in a couple of seconds.
Steps to do it (I have bad skills

After falling down from the wall,
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If done correctly,
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Video by Ghosthunter