Categorie Management and structure

Hi all,

have you got any advise on how to structure the numbers when setting up categories?
I have set up my main categories with 1, 2, 3, 4 etc. The sub categories could be 10, 11, 12, 13 etc.

I have see in the demo shop that they use strange numbers like 201 etc. for sub categories. Is there a reason for this?

Thank you in advance for a little help on this. Really want to get it right from the beginning so it is easy to add new categories in the future without having to change anything in the existing structure.