You may also want to use a third-party website for advertising purposes: with well-placed ads on blogs and websites that match your target audience, you reach many potential customers. In this context, it also makes sense to check website traffic beforehand, since the more people that visit your site means that more people come into contact with your ads.
Glen takes various examples of how simple ideas and websites have gone viral in the past. He made a Feedburner mini-site and emailed a mere six people about it and tweeted the link once. The site had made to the HackerNews homepage the very next day, garnered 500 or so back links in a single day and the domain is now a PR 4. The whole thing was made in less than a day, looks ugly and is not even properly optimized for mobile.
Not all web traffic is welcomed. Some companies offer advertising schemes that, in return for increased web traffic (visitors), pay for screen space on the site. There is also "fake traffic", which is bot traffic generated by a third party. This type of traffic can damage a website's reputation, its visibility on Google, and overall domain authority.