Technically speaking, a new pilot is going to be better at being a pilot than a converted Tech, because a converted Tech will always start out at 8/8. However, there are a couple really good reasons to cross-train people
1) One salary instead of two.
2) Experience gained doing pilot things can be used to increase Tech skills. Otherwise, Tech skills take forever to raise.
3) It's cool.
IronBeer: It will take 40 experience to get from 2/3 to 2/2. That's honestly a few points less than a couple of other wishlists posted already, so it's fine. I think, for cross-training I'll go with Aerospace, and then once that gets to a respectable level Infantry skills. The commander should be able to do everything he asks his troops.