Confused about "Ask to Join Networks"

What is the effect of turning the "Ask to Join Networks" option OFF? I've seen conflicting answers in this forum and other places on the Internet and am now thoroughly confused.

My understanding is, when that option is ON, my phone will automatically connect to known Wi-Fi networks. If am not within range of a known network, the phone will look for other networks and list any it finds, but will ask me whether I want to connect to any of them, rather than connection automatically.

What I don't get is what happens if I turn that option OFF. Willl my phone:

1. No longer automatically join ANY Wi-Fi network, even known networks, so that I will have to go into settings and manually select a network when I want to connect? OR
2. Automatically connect to known networks, and when I'm out of range, look for other networks and automatically connect to any unsecured network it finds without asking me if I want to connect or not?

My concern is security -- I don't want my phone to connect to any random unsecured Wi-Fi networks I might come within range of. I understand that it will always ask me first if "Ask to Join Networks" is ON; my question essentially is, if I turn that option OFF, does it make me more secure, by preventing the phone from joining ANY unknown network, or less secure because the phone will join unsecured unknown networks automatically without letting me know before it does it?

I know I could just turn Wi-Fi off, but I'd rather not do that.

Thanks in advance.