This was maddening earlier on when the game was released and further. One that I really wanted to unfollow was Epistrophy because that quest was entirely annoying with Delamain calling you every two seconds or crashing into you while you were already doing another quest or whatever. To this day, I still haven't done that mission because I don't want all those cab listing in my journal. I do mean to try it again though as I understand that it has been vastly improved.
Other than that though, I haven't felt like I needed such a function.