Hi there,
I’m using a 27"-iMac and I’m thinking about to buy a second screen for development in Unity.
Is this useful to use two screens for development in Unity? What benefits does it have?
It allows you to keep Unity open on one screen while keeping the documentation, MonoDevelop, your design notes, email, etc open on the other.
Is it possible to split Unity-Elements to two screens? Such us ‘Game’ on screen 1 and PlayMaker on screen 2?
Yes.
Be careful about performance though. I used to think I was being really clever having my Gameview on one screen and my Scene view on the other, until I realised that my framerate was terrible because Unity was drawing both windows at the same time…
Ok, but it has no negative effects, if I only use tools like PlayMaker on the second screen or GameView AND SceneView on the second and coding/tools on the first?
Yeah there’s nothing actively wrong with it. (And feel free to use GameView on one screen with SceneView on the other if it doesn’t drop your framerate too badly - I only ran into problems because my scenes are huge).
Ok, so you would say: buy a 2nd screen, because it’s useful for gamedev?
Should the 2nd screen has the same size as the 1st?
Well, it depends on what you could spend the money on instead, but in general, yeah, it’s a good thing to buy at some point.
At the very least you should run them at the same vertical resolution (assuming you put them side-by-side). The mismatch at the boundary between the two will drive you crazy otherwise.
Ok 
Thank you for your help!