I don't close mine up, either. They are free range and I am out in the country. We have the usual mix of southern predators, fox, coon, etc. But we also have dogs and cats that hang around the chickens, and that have killed a large poisonous snake (one that I know of) and numerous rats (the big ones.) I figure a fox would lose the fight and a coon would leave. I have a good sized chicken yard, maybe 70'x100', that at one point had electric wire. The fence itself is very sturdy and 6' tall. I leave the gate open. The dogs got bit by the electric fence when it was on, and never go in there, although it has been off for a year or so. I figure some predators had the same thing happen to them; I used to hear noises indicating this, at night.
At one point I kept the gate closed and the fence turned on, but did not close the pop door to the coop.
Yes, I could lose chickens. And have, before the dogs were so helpful. But my chickens are living a natural chicken life and always have access to greenery and bugs.
It's a personal choice. Lots of people on here give them various levels of freedom, and lots more keep them in Fort Knox. You will never get a consensus to your question.