A space is a content repository. Think of it as a place to keep all the content related to one project. Each space has its own components, datasources, assets, environments, domains, collaborators, and permissions.
If you want to launch several websites or apps that are independent from each other, the best way to go is to create a separate space for each project.
If your goal is to deliver the same content with different languages to multiple platforms (a common set would be the web, iOS, and an Android app), then you can use one space and create multiple API keys to deliver the content.