I've always referred to this sort of thing as Visual Checks. I kind of liken it to what a pilot does when he wanders around the outside of his airplane, kicking the tires, checking there aren't any birds nesting in the engine intakes, pulling bits of bird out of the various tubes from the last time you hit one... that sort of thing. The pilot has no real idea if his plane is entirely airworthy, but he does at least have an understanding that nothing obvious has been missed and he should be ok to at least turn the engine over and go through his pre-flight.
Visual Checking of your software is much the same. It's not really going to tell you if your code is actually working, but a quick debug through a problem area of code might help you spot something obviously wrong as a kind of a sanity check before you go and tell your boss what a great job you've done of your latest task. It certainly doesn't hurt, and can provide a good starting point for a major debugging exercise when you know you have a serious bug in your code that you should walk through, however for the most part you don't gain anything in terms of testing by relying too heavily on visual checks.