I use 550 for a ridge line on my tarp, got the cord for free from a buddy that works for sierra national forest off there 1000 foot roll,
I use home made tree straps with key chain in each end and a extra key ring that i tie inline on the ridge line and use the key rings like a truckers hitch yes i have to stretch it like 4-5 feet depending on length between trees.
I hang a 10-8 harbor freight camo utility tarp on it, also acquired free.
I know I dont have the best gear, but 550 cord works for me but i do stretch the cord as tight as I can.
I have been making my own gear lately and plan on getting good rope, I just keep using the 550 cause its here.
I have used a piece of 550 to pull a civic out of a ditch once it was looped over but it almost doubled in length before the car started to move.