It comes down to the personal opinon. Do you feel like you are out of desktop space, do you want to be able to reference more things at once?
I am a gamer, and I use a primary 1080p with a secondary 1600x900 for referencing things in game/skype/music and that is plenty for me. Is it necessary, no. Is it good to have, sure.
I would get 2 monitors, and add a 3rd if you feel like you need it.