They're just a cutesy form of slang, I don't know that they're worth looking down on. They've been around for ages, although they probably became more widely known when the media adopted "Bennifer". It's just a catchy nickname, like "Ginger Spice".

The only time smushnames or shipping names bother me is when I literally can't figure out how the fandom came up with them, because they make no apparent sense. But I don't hate the concept itself.