As mentioned elsewhere this is probably confusing for more than it is obvious. Why not do away with the Collection and just use a Tag, keyword, etc... and voila. There you have a collection!
Noooo! That's absolutely not the same. One of the nice things about a collection is that it can be completely independent of the metadata.
If you find things unnecessary (or too complex) simply don't use them. That's the nice thing about PM, it gives you lots of choices for your workflow.
That said, I suggest you still play with things a bit. I never really used a catalog before I started beta testing PM6+. Yes, it sometimes took a bit of getting used to, but now I think it actually works quite well. The fact that you can make use of multiple catalogs at the same time is adding a lot of complexity, but something that will be a gepresst feature later on. Some GUI (layout) things need improvement and there are still bugs (hey, it's a beta), but over all I'd say it looks really good (and fast!).