When I'm installing cassette on my freehub, I need to make sure that the spaces align correctly. That is, there are 9 splines on the freehub and 9 corresponding splines on the cassette. My first attempt was just to put it in any of 9 positions but then I found out that one groove on the freehub is slightly bigger and the corresponding spline on the cassette matches it. So in fact, there is only one acceptable position. Why is this like this? Why aren't all of the splines the same size?
Naturally, I managed to replace the cassette, so I ask this out of pure curiosity because to me this "feature" seems annoying because I need to look closely to match corresponding splines, so I thought there must be some smart reason for this behaviour.