I can think of plenty of reasons. Show, fun, curiosity, imagination, etc. etc. etc. o.o
First off, "et cetera, et cetera, et cetera", isn't three reasons, it's a bunch of BS to spout, when you can't think of anything else to say.
I can think of plenty of reasons, because you're to stupid to want a case for your thousand dollars worth of high tech electronics, or too poor to be able to afford one, "et cetera, et cetera, et cetara".
OK,boy, girls, and delinquents of all ages, building electronics, "on the table", so to speak, has been around at least for the fifty years I can remember it. There's even a name for it, "bread boarding". It's normally used to test the viability of a circuit design, certainly not as the finished product. You can use perforated phenolic board, instead of going to the trouble of etching a PCB for the test.
Anyway, when you start knocking out your parents TV with your unshielded junk, creation, post back with pictures of how funny you look with your brand new, pride and joy video card, sticking out of your a**.
Antec has released a line of cases dubbed, "Skeleton", for those whose ego and exhibitionism isn't sated with merely a clear side panel.
Besides, where would you put you CCFL lighting in this caseless wonder? I suppose you could have your little brother hold it over the motherboard, while you're playing WoW.
I do have one question, would you have to buy an anti-static strap for your vacuum cleaner, to get rid of the dust off this monstrosity?