Deejay, the reason I don't like the practice of backlapping is that it removes metal from both the reel and the bedknife without checking which one was wrong. It is therefore "unstable" in terms of the straightness of the line produced. It is just as likely to make the straight component wavy, as it is to make the wavy one straight: all it achieves is to make them match each other. So long as the amount of metal removed is minuscule, it doesn't really matter provided you have both components professionally ground straight from time to time. However if you backlap repeatedly without ever truing up the components, you will probably eventually have big enough waves in both parts to require a greater amount of metal to be removed when you eventually admit defeat and have the parts spin-ground. The cost of new reels being what it is, this can be an expensive mistake to make.
Realistically the amount home mowers are used may not be sufficient for the odd backlap to shorten the life of the reel and bedknife to any important degree. I think the main problem home reel mowers face is occasionally mowing a bolt, rather than becoming wavy over the course of say 20 successive backlaps. To regrind a bolt-bitten reel uses up an awful lot of reel-meat.
