Since you mentioned science-fiction warfare specifically, mirrored armour is considered to be impractical as a defense against weaponized lasers. The fact that lasers use mirrors themselves is irrelevant: the laser being reflected in the vast majority of cases is either low powered (not a weapon), or the mirror is specifically designed for the laser.

In a combat situation a sufficiently powerful laser hitting a mirror will reflect but some energy will remain causing thermal shock which will fracture the mirror. This will also happen if there's some kind of imperfection in the mirror (like dirt) which will allow the energy to be absorbed rather than reflected.

In any kind of ground environment hoping to keep your mirrored armour pristine is, well, as a former soldier, just let me say good luck with that. And that doesn't even consider the possibility that the enemy will actively seek to degrade the mirrored armour's effectiveness.

"Sir, the enemy has deployed a secret weapon that makes our armour vulnerable to their lasers!"

"What kind of high-tech dasterdly device is it?"

"Vacuum cleaners set to reverse so they blow dust out!"

"Damn! How can we defeat such brilliant foes?"