What is the purpose of the two elastic straps on the inside of this fine jacket?

The jacket itself is excellent in terms of airflow, fit and comfort, and construction quality - but those two interior straps just get in the way when putting it on. I'm tempted to just cut the straps out of there but maybe there is a good reason to keep them. I've heard they're supposed to be used to carry the jacket backpack-style around the campsite or when hiking, but if so, why are they so elastic and non-adjustable? Maybe they have something to do with fit or with "non-flapping".

So, keep or cut? I have a feeling I'm supposed to know something which I don't.