Why aren't all pans made like spring form pans, with a removable rim? It would make life so much easier! I have several round sizes and even a square one, which I just found in the back of a cabinet. (The square pan has rounded corners, which would probably be undesirable for large square cakes. Maybe that's the major drawback.) I didn't feel like digging out my small round pan (for baking some extra batter), so I used my 6" spring form pan. So easy to remove cake from pan.
I use my springform pans a lot for regular cakes...before I started decorating my specialty dessert was cheesecake so I have several and I like them for regular cakes because they are odd sizes. I can make an adorable little tiered cake with my 7" and 5".
You're right about the odd sizes.