When you're Small
As we've mentioned logging can be an afterthought when you're just trying to get your first version out the door. But we'd argue that this is the most critical moment to have logging in place. Your very first user is going to do something with your app and if you don't know what it is (or even if this first user has used your app!) you're going to plateau quickly.
This is especially critical if your app is running in a local context (web browser or mobile) and there's an ephemeral quality to these sessions. If you don't capture the moment, it's gone forever.