I love the outdoors but am just really getting serious about backpacking (at an age much later than most); I'm still acquiring gear and figuring things out. So my question is this: Why do vests seem to be so popular as hiking gear? I've never really owned a vest and they don't seem to be too popular in everyday life, so what makes them so great for hiking? Or are they?

I had a couple of conjectures, and I'm curious which if any of these are among people's reasons:
  1. Better mobility
  2. Easy on off and layering (no sleeves getting bunched up)
  3. Keeps your core warm without the extra "unnecessary" weight of sleeves
  4. Regulates temperature naturally when you get hot because blood flows to less-insulated extremities
  5. Lets armpits get air

Basically I'm asking because normally I wouldn't wear a vest, but I thought there's probably a good reason they're so popular. Any big downsides? I guess I worry that during down time my arms would get cold. I would especially worry about this if I were counting on the vest to block wind, but it sounds like many people use them either over or under another wind-resistant layer.

I realize it's a pretty basic question, and I appreciate any pointers in the right direction here. Also, this is my first post in this forum, so sorry if I've posted this in the wrong area.