It depends on your objectives. If you take angel/institutional money, you should at least have a good idea of what billion-dollar-plus market you're going afte

It depends on your objectives. If you take angel/institutional money, you should at least have a good idea of what billion-dollar-plus market you're going after. How specifically you monetize within that market can't always be pre-determined because its a function of a really good product (which takes a lot of morphing/iteration). It's not a good idea to bank on advertising (unless you're building an ad network) or unless you're product has a great context for capturing purchase intent (from which you can do some pretty killer lead-gen/affiliate).