I use pencil only when im doodling important things like character development, outside of that I try to only use pen to challenge myself. No eraser? No problem. Pen teaches you how to better the mistakes that you could of just erased if using pencil.
In the situation of inking though, I use pencil for sketch and primary picture then go over with ink and kneaded eraser for final. Since I am mostly digital I tend to skip the inking process and go straight to scanning and finishing digitally.