If you’re using monospaced fonts for writing code (please tell me you are) spaces make sure that the code will look roughly the same on everyone’s machine.
If I’d used tabs, the second and third parameter might not align with the first.
Also, left-side indentation is only a small part of the overall whitespace in code. You’re adding whitespace even when you write x = y. Spaces make sure that this whitespace around the = grows in the same scale as the indentation.
Yes but it's not your job to make sure your code looks the same for everyone else. If they'd prefer to read it with a different tab size, maybe they're using a smaller screen, or a larger one because of vision issues there's no reason they shouldn't. You can use an optional editor config if you want it to be able to look the same for others.