It does no good to have an effective lock unless you use it. Stealing a bike takes only a few seconds, so being away from your unlocked bike longer than that makes an opportunity for a thief. You might think that having a cheap or ugly bike is a deterrent to thieves. While this may be true, consider what the bike means to you aesthetically, rather than its purchase price. Lock your whole bike.
Many cyclists make the mistake of locking only the front wheel or only the top tube of a bike.
They may return to find only the front wheel or frame still locked. This locking routine is not practical in many cases. The next best option is to lock the front wheel and frame to the rack. Not only is that technique a better deterrent to thieves, on FSU's giant U-shaped bike racks, it decreases the likelihood of your bike being knocked over and damaged. Bike theft is a crime of opportunity.