My main DAW is Logic X.
I also have Pro Tools installed, to take advantage of my control surface (Command 8). The performance leaves to be desired compared to Logic, so I don't use it that much, but it's handy for compatibility reasons, and I try to stay on top of it because PT is everywhere.
I have Harrison MixBus, which I never use. Cubase, if I feel like I need a change of pace - but I don't use it either. I had Studio One but I sold my license because I never used it.
In my experience - and I know it's different for every one - the only reason I ever really "need" another DAW is if I feel uninspired. Instead of working, I start messing with plug-ins and synths. But the problem is me, not my DAW. If I'm inspired, I can't imagine working with anything but the software I know like the back of my hand.
For me the benefit of having a second DAW is that I can launch it and get it out of my system, validating that a second DAW is not the solution to my problem. Every time I do launch Cubase or Pro Tools, I usually get back to Logic within minutes. In all fairness, if I had to pick a real second DAW, I'd pick Logic 9.
On a very pragmatic level - a lot of my music is built in Logic, meaning that I create sounds as I go, adding busses and all. By the time it's time to mix, I don't feel like starting from scratch. And Logic let's me create a new project and import individual tracks, their settings, automation and their assigned effects and busses if I want to - which is the best of both world.
I guess if I recorded bands, it's be different.