The issue that comes up is when you go to add a line to that 'block' it's easy not to notice that it's not actually a block, just a single statement. Then you add another indented line, and now you've got something that looks a lot like a block, but isn't at all!

Of course, as others have pointed out, with some sort of reasonable linting setup or with compiler warnings, you'll probably catch the bug (unless macros are involved), but even so, I feel having something that looks like a block but isn't, adds cognitive load for little benefit.

This works well in languages where whitespace matters