Host filesystem pollution problem
Both virtualization and containerization solve certain problems developers face. There's no real point in installing server-style software systems on your workstation – that kind of software can be installed in a virtual machine or a Docker container. Using this strategy means you don't have to pollute your workstation's filesystem, you won't have software version conflicts, and you can run a different operating system than the one your workstation runs.
The pollution problem is a real concern for developers – they end up with a lot of cruft, or installed software, that they don't use day to day, but that take up system resources. We will learn to use virtualization or containerization to install that software in a way that isn't installed on your host's filesystem.