It's good airmanship to fly to the right of a line feature when following it. However, as a rule it was hard to apply. There are many things that could be construed as 'line features', and there are many aircraft that find themselves going in roughly the same direction as one without necessarily intending to 'follow' it. So it didn't make a very effective rule. No such system, whether rule or advice, will ever be more than a risk mitigation measure, but as a risk mitigation measure it's good to take advantage of it when you can.