Some years ago we descending into somewhere when ATC said cleared to XYZ fix(a certain radial and DME from a VOR) about 50 miles ahead. Captain wanted to continue on present track instead of reprogramming nav unit as it was only a 3° difference in track. I pointed out that using the 1 in 60 rule, we would be almost 3 miles off course by the time we got to XYZ. He reprogrammed the nav unit.