You're leaving out the option of a practice weapon. I don't know if that was common back then, but it's an easy answer to the problem of needing to practice things that will definitely damage the weapon.One such engagement is probably fine, but repeatedly using the blade in such a manner will result in the sword becoming somewhat disfunctional over time.
All those nicks will cause the blade to get caught (on armor, etc), which leaves you open to counter-attack by another foe (longsword is a war sword, not a dueling weapon). Repeatedly removing such nicks and re-sharpening the blade will over time remove enough metal to weaken the blade and make it unusable as a weapon of war.
Fair enough if you can easily refurbish and/or replace your blade (money, labor-saving technology, etc). Not sure the same can be said of Medieval persons.