It's part of a lot of web standards and also commonly used for crypto stuff. E.g. the plain text files in your .ssh directory are typically in base64 encoding; if you use basic authentication that's $user:$passwd base64 encoded in a header; you can indeed use it to have images and other inline content in the url in web pages; email attachments are usually base64 encoded. And so on. One of those things any decent standard library for just about any language would need.