Wifi doesn't work unless I turn it off then on again I have a MacBook Pro 15" with retina display that I use for work/personal stuff and I always shut down with Wifi having been on. When I startup my Mac the Wifi icon looks like it's searching and never actually connects (most of the time). To get it to connect I have to turn of Wifi (on my MacBook, not the router) and turn it back on, then it connects pretty much right away. What's the issue here? It's very annoying.
Old preferences hanging around after upgrade can cause issues. To force a rebuild of the preferences open Terminal and do:

cd /Library/Preferences/SystemConfiguration
sudo rm NetworkInterfaces.plist
sudo rm com.apple.airport.preferences.plist
sudo rm preferences.plist


then restart your machine.