Not sure what you are asking. Why use 140 instead of 160 Kbps? 140 produces smaller file size, and is practically transparent as far as I know. Or you mean why

Not sure what you are asking. Why use 140 instead of 160 Kbps? 140 produces smaller file size, and is practically transparent as far as I know. Or you mean why reencode later from lossless again, if a better codec appears? If it will be better, it will offer some benefits (smaller size, faster decoding and so on). So why not?