Is it necessary buy a screen protector if I'm going to use a stylus on my ipad?

Your finger is not what the screen protectors are protecting your screen from, so yes. In fact, a stylus is often rougher on your screen than a finger; it just doesn’t leave oily smudges the way skin does.

The only way to really get around a screen protector is to assume the risk of scratching the screen… unless you never transport it. Personally, I take my tablet places, and my phone spends over half it’s life in my pocket (often with metal chips; I’m a machinist, and those chips get everywhere), so I use screen protectors.

My friend used an ipad every day at uni with a stylus. He used a note-taking app that would scroll the page up as soon as you got to the end of the line, so he was always writing on the same part of the screen. The stylus eventually wore down the screen, I suppose whatever protective layer is built in to the glass, and so there is now what looks like a permanent smudge patch but is actually worn through. So yes, after witnessing that experience, I would recommend a screen protector.