For myself, I mainly subscribed to support the WinCustomize site and was thinking of the benefits I derive from the site itself. (I've subscribed to other sites for the same reason and /or for access to premium content so it's a concept I'm comfortable with.) Skinbrowser does have its benefits, however. The message board and WC site are quicker to load and navigate with the skinbrowser. I haven't used the chat interface myself, so can't say how that is. Um, what else? Well, there's the premium skins that subscribers will have access to. Apparently the first should be released soon.
While one also can use the sb on the net at large, it wouldn't be my preferred means of browsing the net so I wouldn't look to it as a substitute for your regular browser.
I figure the main deal is a subscription helps support the WC site. The skinbrowser is a goodie thrown in as a thank you which can help you use the site in a more efficient manner.