So you ask, 'Who's got the time for this?' If I had to deadhead things in our yard, I wouldn't have time for much else. Therefore, I do not deadhead. The only deadheads I've ever cared for are the Grateful ones.
For those of you who do there are many benefits. The main one is many plants will re-bloom throughout the season when deadheaded. Deadheading is very easy to do. Cut the spent flower heads off and compost them. Every plant is different. Some may have long stems that need trimming; others may have short little stalks that require only popping off the flower top. One thing you can do to save time is if you have a mass of spent flowers, like campanulas, use your weed-wacker to do the job.
Some plants you do not want to deadhead, like coneflowers. Coneflower heads are beautiful in fall. We use them to make fall wreaths in September. The finches also come to the coneflower heads so make sure to leave them up. I also leave astilbe heads up. The reason being is that many flowers add another interesting dimension to the garden even when they're dried and dead. The seed heads of many plants are quite interesting, such as, astilbe, gaillardia, coneflower, and sedum.
So if you must, rock on you Deadheaders! As for my garden, it's survival of the fittest.
P.S. Pigpen was always my favorite Deadhead.