Another argument not yet mentioned is that having spaces rather than TABs gives
one flexibility in (probably only temporarily) wedging in a control line
governing a set of sub-blocks at some "half-indent" amount (such as only 1 or
only 2 spaces). You can do some `if` or `when` for example. It could also make
certain patches that effect such changes smaller (by adding one line instead of
adding 1-line and shifting a ton of stuff) and more robust (since diffs are
usually contextual and this would require less context to match). Admittedly,
not a huge deal and a very rare case compared to reading code everyday, but
still something concrete which would not be possible with exclusively TAB
indents.
