I use one for stuff I need to take into work with me, and I remove it and carry it on the bus with me. The other I leave locked to the rack most of the time. I would probably use both even if I wasn't such a junkaholic for the reason JPprivate gave, just in case I need to pick something up on the way home. My goal is to make bicycling as practical and hassle free as possible so that I'm less tempted to drive. Not that motorcycles (my main motorized transport) are all that hassle free either.