I'm 550km away from where I live this weekend. I'm keeping extra pokemon I might throw away bc if I trade a pidgey caught here for a low iv Ralts that someone else catches where we both live....drumroll...the person trading the Ralts gets +3 Ralts candy. I get the one Ralts candy bc I'd immediately transfer it and +3 pidgey candy..
The 100km is the cap on distance caught from each other in regards to bonus candy awarded.