The advantages I see are 1. Fewer keystrokes: An obvious benefit, but perhaps better than one might think if, like me, you mis-key what you're intending to type, every 10th curly brace or so and have to spend a few extra moments wrestling with repositioning things and 2. Fitting more code on the screen feels like it gives me a small, but not insignificant, mental boost, by increasing the likelihood that I can see related bits of code without having to scroll to find them.
I worked as a professional C# developer (with curly braces) for about 7 years before starting to code all personal projects in F#, and have used Python in numerous continuing education courses, and I immediately preferred significant white-spacing, but it's probably just a personal preference. I've never even thought of the potential for increased software defects, so I don't think that would be a likely issue for me. I'm certain that the type system in F# all but eliminates the chance that you'd get a code block out of place and still have your software compile. Perhaps that would be a more likely problem with Python, but still not one that I've encountered. I try to adhere to the "Make your methods (or, functions) small, then make them smaller than that" school of clean code which might be a part of the reason why I've not run into indentation problems. I've also not tried integrating with a team which has used different code editors with potentially different whitespacing configurations, but that doesn't sound difficult to overcome.
The biggest problem I've probably ever had that is at all closely related to this conversation was maintaining old Delphi/Pascal code, which as I recall did not have significant whitespace ('begin" and "end" I believe, blech), but also the coding environment lacked a feature to automatically fix code indentation, and some of the monster methods in the legacy code that I was maintaining was nigh unreadable due to horribly mis-aligned indentation.
I would never advocate for adding significant whitespacing to an existing language.