Placing related controls on a page

I have been designing a page in WPF (Windows Presentation Foundation) wherein I have two combo boxes, the first of them contains a list of categories and the second contains a list of sub categories.

I have placed them in such a way that they are adjacent to each other as opposed to one below the other, as we see in most of the user input forms.

Since there are a lot of other settings that are available in this page, predominantly containing the above mentioned flow, I would be really glad to know the pros and cons of this approach of placing the related inputs adjacent to each other.