What does "Upload to My Photo Stream" do?

I'm currently sharing my iCloud photo Library among several iOS and OS X devices, works great! However, I don't want every single photo I take to show up immediately to the library. I thought the purpose of the "Upload to My Photo Library" setting would solve this exact issue. It's turned OFF on my iPhone but as soon as I take a picture, it shows up on my iMac (this is in my house on same wifi network, so it happens pretty fast). The setting literally says "Automatically upload new photos and send them to all of your iCloud devices when connected to wifi". So, if I turn it off, it should not automatically upload new photos, right? What am I missing?