The problem with this method as 727kid said above is that it only includes 60hz and 1000hz. 60hz is too high. On many high end SQ systems the crossover points are going to be below that anyhow. But even if they're not, if your sub happens to not distort at 60hz but distorts severely at 35hz what good did it do for you?
1000hz is the same issue. That's very low on the midrange scale, so what about 1001hz through 20,000hz? Do we just not care how it sounds through that huge range?

You do not tune a stereo that is expected to play 20hz-20,000hz with only 2 poorly chosen tones.