Why? What would the advantage of that be?? The disadvantage has been discussed in this thread.

One of the pages that talks about this: Hooks.

Sorry, but that page only contradicts your argument. Nowhere is a guarantee made as to which context the hooks are called in (the documentation of the callback on_osc_seq even explicitly says "The default should be to return an empty list."). The page explicitly says "All of these hooks must return a boolean value. ... When in doubt, return a false value (preferably ())." As per Truth and Falsehood, the false values in Perl are: "The number 0, the strings '0' and "", the empty list (), and undef". A list with one element is true, and so again, return 0 is not always false!

Further I argue that your interpretation of the intent is wrong. If the author of the documentation wanted you to return 1 or 0, or if the hooks were always evaluated in scalar context, he/she would have said so. By deliberately telling users to return the empty list (), they are, for example, keeping the door open for the hooks API to be more easily extended in the future - hooks could return multiple values.