This can be useful for more trivial actions, the consequences of which would be pretty minor for the user. On the other hand for irreversible actions, as the a

This can be useful for more trivial actions, the consequences of which would be pretty minor for the user. On the other hand for irreversible actions, as the authors put it (and ones more drastic than those mentioned here), a dialog, modal or otherwise, is perfectly warranted. One more click hardly makes any difference in time, and it brings up a brief little moment for reconsideration in case the user doesn't immediately realize they're doing something potentially unwanted.