>>7714966
You should never need an eraser while sketching. Draw lighter and restate the line if it's not what you want, spend more time measuring and placing guide marks. You're probably chicken scratching so any line or form gets lost in the sea of all the marks you've made.
I only ever use erasers if I'm inking something.
If you need perfectionism and refinement, then do multiple drawings and take time to copy with a grid or trace.