The categories would be a base idea; somewhere to build from. You choose a certain Category to build from. Less like 'taking a level in fighter' more like 'I want to make a meleeist who can X, but he's a meleeist so I'll go with this Category'. They won't have a mechanical effect, beyond helping beginner players figure out what they want to do with their character; or shouldn't, at least, depends on how the system works out. We might not use them. All depends.