Traffic allowance: Unlimited
All the features I've detailed to this point are valuable to the web hosting experience, but none matches the critical importance of site uptime. If your site is down, clients or customers will be unable to find you or access your products or services. It doesn't matter how great the features are, or how good it looks; if your site is down, it might as well not exist.
The most obvious and popular reason for a VPS is to run a single website, or multiple websites. However, you can use them for pretty much anything that requires access to the internet – such as a web application like Nextcloud to run your own Dropbox alternative – or to create your own virtual private network to better secure the internet connection of your PCs and mobile devices.