Guess I'm in the lots of different tools for different jobs camp, let's see... I have two WSMs, a Performer, a 22" kettle, a Smoky Joe, and a Genesis gasser. The gas grill was the last one that I acquired, but after a long time of hesitating to do so (and being influenced by growing up around el-cheapo gas grills that sucked and rusted out in no time) I realized that it definitely does fill some voids. As others said, it's quick and less sensitive to bad weather or changing winds. It takes hardly any fuel or time if all you are needing to do is make a few hot dogs for some hungry kids that just got done swimming or whatever.
The other thing that I haven't seen anybody else mention but was a reason for getting a good gasser "here" is that we do a bunch of canning, freezing etc. from our gardens and sweet corn patch and such outdoors at our cabin. (Cleanup is way nicer when all you have to do is hose off a concrete patio, vs. taking all that mess into your kitchen!) We already had a Camp Chef outdoor burner there to do much of that work on, but adding the Genesis gave me another platform that is helpful with that stuff. It's an advantage to be able to put something in there, set it at 350 degrees or whatever and know that it will run consistently without babysitting while you're busy with other stuff.