At this point, a launch is just a means of propulsion for a coaster, like lifthills are (and hey, there are plenty of parks out there with half a dozen lifthill coasters or more). Unlike lifthills, a launch allows the coaster to reach any desired speed without adding any height, so they are very useful and versatile if the park can afford them. And as said above, they are much easier to work into a story too. There's possibly also an argument of capacity, as a launched train will complete its circuit and be ready for another trip much faster than one that lumbers up a lifthill for half a minute, but I guess it makes a pretty small difference compared to aspects like efficient ride ops.