It’s an issue when generating python, I can tell you from experience. It’s also a pain to not be able to safely rely on an auto formatter

Have you never tried to paste python code from the internet into an editor? At least half the time the indentation is screwed up and I have to go in and figure out manually where to put the spaces in. Indentation gets screwed up by pasting in other languages too, but with those I can generally tell the editor to reindent and it can because the information is included in the source code.

Python's significant indentation does have real costs, but they mostly don't affect experienced programmers working on real codebases in real editors or IDEs. Rather, they are things like, it makes the REPL more cumbersome, and newbies sometimes find that code they copy-paste from the Web mysteriously fails to work.