Let’s face it if you are hiking in bad weather and you’ve already accepted the fact that hiking means discomfort then using a poncho-tarp as clothing and shelter is a real possibility. There are two real challenges.  ponchos, in blustery weather, blow everywhere and do not offer much protection.  when transitioning from poncho to tarp getting the cordage right can be a challenge.
This weekend I took the family to a soccer tournament. The morning of the second day we saw terrible rain and for the most part it was raining sideways so the colemen tent was almost useless. I ended up using my poncho as a tarp to deflect the rain from the side but it was cold, I only had 550 cord, and my fingers simply would not tie a knot.
In hindsight I could or should have used plastic s-biners. I suppose I could have used smaller cordage but I did not have any on me. uhg.