Word processors such as Microsoft Word are said to be WYSIWYG: what you see is what you get. In a sense that’s true, but in another sense markup languages such as HTML or LaTeX are really WYSIWYG.
With WYSIWYG programs, what you see is what you will get visually, if all goes well. If you think of the computer file as simply an intermediary between your keystrokes and paper coming out of a printer, the paper is “what you get.”
But more fundamentally, what you get when you edit a file is a file. And the relationship between your keystrokes and the changes in the file could be quite obscure. With text files, such as files containing source code, what you see is what you get in the sense that the characters you see in your editor correspond directly to the contents of the file.
Sometimes I’m quite happy to be ignorant of how my keystrokes correspond to file contents. When I’m cropping a photo, for example, I’m grateful that I have a visual interface and can be safely ignorant of the layout of bytes in a file. But for other tasks, text files are simpler because there are no mysterious forces at work: what you see really is what you get.