I've had a WIFI network for several years now and never bothered to put in a password. I didn't mind if a neighbor used some of my bandwidth AS LONG AS I still had decent upload speeds. I "borrow" bandwidth from time to time when I travel and I am conscious about using it just for quick email or light browsing - no video, software, etc.
Over the past few months I noticed my connection getting very sluggish. I finally logged on to my router and was shocked to find not just a couple of neighbors had been logging on, but over a dozen computers had logged onto my system. A couple of them had the names of teens around the block, and that is where I guess my bandwidth went.
So I finally encrypted my network. It's a little disappointing in a way since I don't mind opening my network as long as it isn't abused.