To engineers that's the ho-hum process that happens after some genius creates a great product. To the rest of us it's the way we find out about a product that could be great, understand why it would be great for us, and get it in our hands with the functions, quality and sex appeal that make a great idea brilliant.
Brilliant products are few and far between. At Apple, Jobs has been able to produce a regular string of them.
With him on leave there's a good chance the also-rans will catch up to Apple and that the flow of innovations that have kept it ahead in the past will languish in committees of risk-averse managers rather than going through the ruthless triage and nitpicking attention that drives co-workers crazy but often makes the end product far better than it could be without a monomaniacal aesthete driving the process.
If Jobs turns out to be a great CEO, the people or processes will already be in place to be sure the innovations continue to flow without interruption.
If he's an egomaniacal control freak who needs to be the only fulcrum on which Apple's creative power can rest, his medical leave and longer if he chooses not to return will be a bad time for investors. It will also be a dull one for geeks hoping for more creative disruption from a company that has delivered consistently on that promise only when Jobs has been the one doing it.