It certainly isn’t benevolence, but the airlines simply accept that some tight scheduling practices simply aren’t safe, so some flights get a 3rd pilot.
Take a round trip from NY to the Caribbean- it may just be doable with 2 pilots, but why risk the crew going fatigued down route and then having to cancel the northbound flight, when you can put a relief pilot on board, and operate more reliably?
My airline recently started service to a Caribbean destination a few times a week, where the schedule had a crew deadhead outbound, then operate the leg back home. After having significant delays when the first few crews were too tired to fly back, it’s now scheduled as a 48hr layover.