Explanation of URL/Category Link problems needed, please

[Bronxgodzilla +]

Hi all. I am new to the construction of things but piling on the work as fast as I can. Great Product!

I am just building my first store, looking to purchase various types of mods -- but I just came across something I do not understand in the Admin area, in the Section ~ Managing Categories / Category setup / Category Link -- can those knowledgeable amongst you please tell me what it means and what Gotcha's or liabilities the Note is warning me about:

"Entering a URL here [for the var called 'category link'] will cause anyone clicking the Category Link to be re-directed to that URL. Please Note: this prevents the placing of Ads in this Category."

Will someone puhhhhleeasse explain this? The Good and Bad? As some of my category links (not all) are sub-domains <http://www.my.domain.com> it would appear it is saying I **cannot** place ads on or at sub-domain level when linking to it. Doesn't make sense.

Why Not? What's a work-around? I find it hard to believe. Is this saying, in essence, that category links will ONLY call up a single local html page?

Tell me it ain't true, boys :-) And why.

Thanks