What does this "conversion" mean? The ultimate objective would be for some $$$ to leave the user's wallet and go into the company's wallet, and I am not sure if this actually happens.

First off, people who give out their email easily would typically do so on plenty of other sites and your subsequent upselling emails are likely to get lost in an inbox flooded by spam.

Second, I'd argue that people who have the most disposable income or influence on purchasing decisions made by their company are also those whose time is limited and are too smart to fall for such tricks, so the majority of leads you do end up with would be worthless.