what do you do when you don't have enough pci slots or they're covered by a card and you need to use those slots?
then you cant use it. or switch it out with another pci card that you can do without. perhaps a wifi card can be interchanged with a usb one?
heh it doesn't get any simpler than that. if you can't fit it then you can't fit it. you will need to remove one to fit another.
oh yeah! how about tv tuner on a stick? lol http://www.newegg.com/Product/Product.aspx?Item=N82E16815260023
Believe it or not some peripherals still use the old pci bus. And some users might even have old vga cards that use pci slots... can't imagine anyone still using that though. It's mostly used for extension cards and such...