Depending on the title, you may not save much. BIN's typically have some overhead space, and on a pretty packed disc (like a Final Fantasy or something) the end result can be an image over 700MB.
Your idea is not without merit tho. I actually am doing this with a DVD-RW drive. In this case, it's a godsend. Throwing several images on a disc is nice (~4.3GB each disc). I got Final Fantasy IX *and* Xenogears on a single disc. Being a DVD disc, the read time and seek time are very good, and it plays just like it was off the hard drive (and considerably faster than off the original CD)
The only problem is games with CD audio tracks. I have a couple of older games with them, and when ISO'd (meaning any form of archiving like BIN etc) the audio tracks are preserved but don't play. In my titles this is just music tracks that I could care less about anyways, but if there's one where the CD audio is like important, that could be a problem.
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-SSZ