I'm of mixed minds here.  On one hand, I do agree with @hamogu that this is a good example of how functions are useful.  *But*, equivalencies can be a tricky thing, and having a concrete example like this might go a long way towards people understanding it.  

Maybe we can have our cake and eat it too, by actually using the equivalencies *inside* this function (with a comment about why we are doing this)?  It also might be useful to reference the Quantities tutorial, which talks about equivalencies in a bit more detail.