Richard, the basic function of the pre-launch phase is to attract and build an email list of potential launch phase sales prospects, either via your individual efforts or with the help of your JV partners or affiliates, usually with product topic related free content and related bonuses. The content (and, typically, the mention and build up of the upcoming product to be launched) is delivered systematically, usually via email optin list, during the pre-launch phase ... building up to launch day, when the pre-launch list is usually given a hour or more advance notice and ability to purchase during an 'early bird' or 'early notification' time period.
Frank Kern is a master of the pre-launch, pre-selling so effectively that he often sells out high ticket launches just an hour or 2 after going live. Of course, his self and product brand developed over time has a lot to do with the results, as well as his high level associations ... but his mastery of the pre-launch surely helped get him there.
The aforementioned is a very basic explanation ... and mentions only a few possible scenarios, but it should get the point across.
As far as WSOs ... yes, that could be a very helpful part of the pre-launch process ... especially in terms of seeing how well the product is received, and to garner early positive feedback and numbers to present during pre-launch and to attract JV/affiliate partners.
Still a coffee short, here ... hope that helps.
Cheers,
Mike Sr