I agree with ortega and blurblock on this. Actually these two lenses compromise each other very well, and due to the overlap range, you don't need to change lens too often. When shooting landscape and stuff like that, the 17-40mm works very well. But it can be used for wedding/events and etc. too. When shooting events/street candidates, the 24-70mm works better (imo), and it works okay to shoot landscape too.
So whenever you go out with either lens, you'd end up with very good coverage for whatever you shoot at
I'm using a 16-45mm and a 28-75mm (hope it's a 24-70mm though), and I only carry one of them during outings.
I have both the 17-40 F4L and the 24-70 F2.8L, and yes to me it is practical cos I figure I use the 24-70 F2.8L a lot (yea, the weight kills sometimes too :sweat: ) for general shots a,d 17-40 for wide scenic shots... ;p