There are at least two scenarios where such a service may come handy.
One, if you want to share a bunch of web URLs with someone, instead of putting them all in an email message, what you may do is create a single slideshow with all these URLs and pass them along as just one page.
The other usage is around browsers that still don’t support tabs (like Safari for the iPad).
We all have own list of favorite sites that we like checking multiple times in a day. Desktop browsers have tabs so you can open all your favorite pages in one shot but it’s not so easy in the case of non-tabbed mobile browsers (like the iPad).
BridgeURL offers some sort of a solution here – you can package all your favorite sites as one page and then browse them one-by-one in the same Safari browser window.
The service uses IFRAMES and therefore with not work with sites that block frames (example). Also, the navigation is currently not very touch-friendly but I hope it’ll improve in subsequent releases.