Still not what I was hinting at. It's more a way to show the other players what kind of class you are going for so that they don't go and do the exact same thing. Picking three skills to excel at shows what sort of character you are going for. Example:
Five players make a character each. The first three choose the following.
One-Handed, Light Armor, Sneak - an assassin.
Pickpocket, Lockpicking, Sneak - a thief.
Two-Handed, Heavy Armor, Block - a warrior
The two remaining look at how the group looks and choose the following.
Restoration, Destruction, Alteration - a mage
Archery, Light Armor, Illusion - an archer or hunter.
Following this easy method the group have a good dynamic, each tending to some of the other's shortcomings. Of course it is also up to discussions, since some players might have a very definitive image of their character (as I do). It has nothing to do with game mechanics, it's just an easy way to build an interesting group where no one needs to feel like a fifth wheel and even create some interesting dialogue between the characters.
Also restricting restoration in that way wouldn't be all that swell. The fact that a mage can heal the others while they fight is a bit of the point with restoration as well as making the recoup from a broken bone a lot shorter.