I have the 24-70, and its a must have lens for me, but mainly just for one use case: when shooting events at my kids' school, there is no time to fuss around with lens changes etc, and I had better not miss any shots or else I have trouble when I make the yearbook pages. I use the 24-70 for indoor shots (head shots, environmental portraits and small groups) as well as big group shots outdoors. Otherwise outdoors I use the 70-200.
For my family, hobbies and travel, I don't use zooms at all. Well I might start using the new 70-200 f/4 now but I certainly use no mid range zoom. For my kids I use fast primes which are not only smaller and lighter than the 24-70, they also give me some creative options, like the 85/1.4 at f1.4. And it does not matter if I miss any shots when I have the "wrong" lens on my camera. When I travel, I generally take just my Zeiss lenses which I love for this purpose and shoot 90% with the ZF35/2. I would not dream to carry around the 24-70.
As a general comment, it is usually best to buy a lens with a specific need in mind, not just to cover some perceived gap in the bag, but I don't always follow my own advice.