One of the biggest problems that a designer encounters is what I call designing into the void. That is, making design decisions based upon the gut-level inkling that you may like to do some undefined thing which you haven't thought of yet with it during later periods of design. Designing into the void is making decisions before you have any reason to make them. It's, IMO, integral to design. Many, if not most, of these Void decisions will be cast away as the design comes into greater focus. You'll find that what you thought may be useful (though you had no idea *how* it would be useful) actually isn't useful and you cast it aside.
I've done this concerning character statistics in Worlds Apart. Traveller has the following stats for all characters which I'm going to use wholesale:
Strength (Str): A character’s physical strength, fitness and forcefulness.There is also another statistic called Psionic Strength (Psi) that only comes into play when the characters have an opportunity to see if they're Psionic. Worlds Apart has no psionics (we've got magic, bub) but there is a need for that stat, reskinned. So Worlds Apart has Magical Strength (Mag).
Dexterity (Dex): Physical co-ordination and agility, reflexes.
Endurance (End): A character’s ability to sustain damage, stamina and determination.
Intelligence (Int): A character’s intellect and quickness of mind.
Education (Edu): A measure of a character’s learning and experience.
Social Standing (Soc): A character’s place in society.
Now here's the designing into the void bit. I'm going to have all characters have a Magical Strength. Why? Well, I have no idea really, but I think that sometime down the road (when I get to designing spells) that I'll really want to have a stat that I could use as an opposed stat for things such as resistances. Now, will I actually use Magical Strength in that way? I don't know, but as of right now, I have the option because I've designed into the void.
I think it's a good decision even though I have absolutely no information to make such a claim. We'll see. :)