One other advantage of reflex sidewalls is that they cover the legal requirement for side reflectors (which exists in many states and cities, including here in California), so you don't need to put spoke reflectors on your nice road bike. In practice, this rule is never enforced (at least around here), but as a commuter I like to always stay within the law, and reflective sidewalls are cheap, light-weight, and harmless.

With wider tires, like 37 or 45 mm, the reflective strip is at an angle, and actually shows up pretty well from the front or rear as well as the side, so I think they have some utility. They are no substitute for a headlight and taillight at night, but are much nicer than spoke reflectors or useless front reflectors.