Used to, now I don't. First, it can wash off the rub. It doesn't add much flavor, that's what the rub is doing. If you cook the ribs right they'll be plenty moist. Every time you lift the lid you lose heat and extend/alter the cook.
And the most important reason, I'm lazy!
I'd rather be lifting a beer than lifting the lid.
after taking DAL (dead ?$$ last) at a contest with ribs, where I was spritzing and taking so much care of them, I figured it wasn't necessary and haven't since.
I just spritz with apple juice two or three times towards the end of the cook. My best ribs turned out when I was busy and only spritz the ribs when I foiled them.