The scope of TFA is data modelling, where it advises to use more descriptive data values, such as enums or happenedAtTimestamp.

However, personally I agree with the advice, in another context: Function return types, and if-statements.

Often, some critical major situation or direction is communicated with returned booleans. They will indicate something like 'did-optimizer-pass-succeed-or-run-to-completion-or-finish', stuff like that. And this will determine how the program proceeds next (retry, abort, continue, etc.)

A problem arises when multiple developers (maybe yourself, in 3 months) need to communicate about and understand this correctly.

Sometimes, that returned value will mean 'function-was-successful'. Sometimes it means 'true if there were problems/issues' (the way to this perspective, is when the function is 'checkForProblems'/verify/sanitycheck() ).

Another way to make confusion with this, is when multiple functions are available to plug in or proceed to call - and people assume they all agree on "true is OK, false is problems" or vice versa.

A third and maybe most important variant, is when 'the return value doesn't quite mean what you thought'. - 'I thought it meant "a map has been allocated".' - but it means 'a map exists' (but has not necesarily been allocated, if it was pre-existing).

All this can be attacked with two-value enums, NO_CONVERSION_FAILED=0, YES_CONVERSION_WAS_SUCCESFUL=1 . (and yes, I see the peril in putting 0 and 1 there, but any value will be dangerous..)