What is the benefit of a good transport?

So if it is about jitter is that something that new technology has improved upon or is an old (say early 90s), high quality transport more or less as good as any newer transport?

Thanks everyone for your responses, especially Shazam. I'm still wondering if it's a technology where new may be better or has it peaked and new doesn't really mean better. I currently use the toslink connection from my mac to my krell studio 2 dac playing lossless files and it sounds really good, but I still think it sounds better when I use my kav300cd - I don't know if it's the cd player's dac or if it's the transport, and the cd player is out for repair so I can't test it yet by using the digital out to the external dac - I do know my sony za20es used as a transport to the krell dac doesn't sound as good as the all-in-one kav300cd.