I have had the Galaxy S2, Note 2,3 and 4 and on each have used the Spigen SGP screen protector, with my work (construction) there is always dust/damp conditions and a big need to protect my phone.
Right now I am using the Spigen screen protector with a shocksock and also a zip tie bag if I'm in very dusty/wet conditions. What I have noticed is with my LED cover and S View cover, over time there are screen marks from where the window of the cover is closed which makes me think without a screen protector in my trade is a no no. I understand that a lot of people work in a lot better conditions but for me, I definitely need a screen protector.