According to a tweet by Ryan Jones (via Cult of Mac), iOS 11 will learn which networks are good and which are bad. Basically when it detects that it has problems trying to connect to a particular network, or when it provides a spotty connection, it will remember it and in the future it will no longer connect to them.
After all what’s the point of automatically connecting to a WiFi network if you’re not going to get any internet or a poor connection, right? iOS 11 will also mark which networks have autojoin disabled. However the downside is that based on the feature at the moment, you will have to manually join the network yourself in the future should you choose, for whatever reason, to connect back to it.
We reckon that this is something you’ll also want to keep an eye out for because just like WiFi assist, it might end up with users who eat more into their data than they would like, which in some cases could lead to overages.