Frankly, the reason its advantageous is b/c there are people who are looking for more than sex, they want a partner. And partners who can show restraint and good judgment, or at least the capacity for, is damn rare. Not immediately screwing something that moves because you can is one easy measure of whether someone might be able to put off immediate gratification for longterm reward. Its actually one of the simplest weeding out methods b/c it is such a simple thing to walk away from. The fact that so few can, or want to, makes it a pretty decent triage tool, IMO.
Second thoughts can generally be amended with judicious action; injudicious actions can seldom be recovered with second thoughts.
--Cyteen by C.J.Cherryh