Lost keys are likely to be found in places you frequent. Sometimes this won't provide much information about where the matching lock is; sometimes it'll provide a great deal. There's a big difference between losing your house keys in a coffee shop twenty miles away and losing them in your driveway.

Generally I think I'd be more concerned about car keys than house keys; not only will you typically not stray far from your vehicle when using it, but testing for a match looks a lot less suspicious and many keys come with features intended to make it easier to find the matching lock.