I hope so. Because otherwise you are not learning real mathematics, just rote memorization. It is not good because that is the mathematical equivalent of a code monkey.
http://wwwf.imperial.ac.uk/~buzzard/docs/lean/sandwich.html
and if you click on a line in the proof, and then on a little grey rectangle, you will see the state of Lean's brain at that point in the proof. But the proof is just the normal proof and a student writing the proof in Lean has to just write the normal proof, but in Lean's language rather than in mathematical English.