Thread:Btd456Creeper/@comment-15575766-20150313000733/@comment-28857013-20150314164624

Or to simply put, it's:
 * Troublesome. There are a lot of restrictions regarding the use without quotes that could be simply solved by adding a pair of quotation mark.
 * Impractical. There's no difference between using both anyway, but with quotes you do see things better.
 * Unsafe. This may not be your concern, but for real coding, doing this could easily let hackers escape the attribute just by having a space and stuff. While using quotes aren't any better, with escaping (Yes, escape to prevent hackers escape) it could solve the hacking problem.

While some said "When unsure, use quotes", many do prefer and highly recommend "Even when unsure, use quotes anyway".