on pi3 ap/client uses the onboard wifi for both... ap+client uses a usb wifi dongle as client.. the onboard has little range so a usb comes in handy when you need to connect to a hotspot
my long range setup
https://www.dropbox.com/s/q8a0k1mmusy5sw...1.jpg?dl=0
my long range setup
https://www.dropbox.com/s/q8a0k1mmusy5sw...1.jpg?dl=0