The real range of answers is only limited by your imagination. There are an innumerable amount of things you can do with a spare bit of cordage. One use that I can see for it in your picture is as a replacement for your rubber band around the tent poles.
The most likely intended use is to secure the sharp end of an ice tool. The nylon loop at the bottom right of your second picture is to secure the head of the ice tool. If you threaded the head of the tool through there it would probably just reach the abrasion resistant batch that the cord in question is mounted. This would also allow the compression strap to secure the handle of the ice tool, and keep the sharp bottom end of the ice tool firmly next to the extra thick abrasion resistant patch. Granted this would also point the sharp end of the ice tool towards your arms which probably isn't ideal....
The OP posted a comment that identified the pack as a Walkabout 65 made by Halti. I wasn't able to find that exact pack on their website, but I did find their Discover 45 pack.
As you can see they have the same type of cord directly above the tool loop like I'd expect to secure the end of ice tools. I think the apparent forward angle I saw in the OP's photo was an artifact, and the cord is for securing the end of an ice tool.
Given that it is above the mesh pocket at the side, my guess is that it is for walking/ski poles.
If you need to put the poles away for a short time (for example, a traverse using your ice axe, a river crossing), you don't need to go to the trouble of loosening the compression straps (the ones holding the tent poles in the photos above).
Mesh pockets are often used for water bottles, the mesh is to allow the condensation on the outside of the bottle to evaporate and not collect inside a regular pocket.
Given the proximity to the mesh pocket, the strap may be intended for lashing the top of the bottle to the pack. Lashing the top of the water bottle helps keep it from moving around or from falling out altogether.
Depending on your activities, this may or may not be necessary. So to paraphrase @Erik, use it for whatever you need.