I answered for my wife. She doesn't usually want to watch it together, but sometimes we do and, if I've chosen the porn wisely, it can be a big turn-on for her.
She's totally cool with my watching porn by myself. I want to have sex every day (often more than once) and she wants to have sex about twice a week. She understands that when I masturbate with porn, I'm not actually fantasizing about having sex with the actual people in the videos, just about having the kind of sex they're having.
The only times porn ever negatively impacted our sex life were a couple of times she spontaneously wanted to have sex in the evening after I'd masturbated multiple times that day (while watching porn). Since then, I've made sure not to masturbate after about noon if there's even a slight chance she might want to have sex with me that evening.
I've always been open with her about the things that turn me on and the types of porn I like. She knows she's always welcome to check out anything in my collection - although she hardly ever takes me up on that!