The FI at my local aeroclub in France told me that it's always good
airmanship;
Low Flier - that doesn't mean that the rule has to be observed 100% of the time. There might be occasions when it's not feasible: for instance on a survey/photographic flight, when the photographer (sat on the right) might need an unrestricted field of view. In that case, a good lookout is of (even more) importance. Just because there is a rule doesn't mean you can relax assuming that everyone will stick to it...
Same goes for the VFR cruising levels mentioned by
Heliplane; on the Continent they're semi-circular (i.e. FL15, 35, 55/FL 25, 45, 65, etc.), not quadrantal, and I do observe them (unless I have to climb above one of the many MIL low alt zones), but I've come accross other aircraft who don't! Incidentally, they're usually the same people who aren't on a Flight Information Service frequency either...
Cheers
