Personal preference.
I have a bow that has a two piece quiver so it never comes off. I prefer to shoot with one on so I can grab another arrow if needed and it's right there. Some like to use removable quivers and attach them to the tree (with an extraquiver mount)and still others like the hip quivers.
My other bows have removable quivers but the only time I remove them is for transport. Like I said I like the arrow right there in front of me. I don't have to change hands, move or twist my body to get another arrow. I just reach with my shooting hand, pull another from the quiver and put it on the string. All of this can be done with very little movement and you can keep an eye on your target. (assuming it hasen't run off after your first arrowmissed
)