An overlay showing exactly what units the enemy is building.
What buildings the opponent is making (e.g., a hidden Dark Shrine or Spire). Army Movement: starcraft remastered maphack
is the most effective way to confirm it. Look for these "smoking guns": Selection through Fog An overlay showing exactly what units the enemy is building
External observers and bots
Proactive strategies like drops or cloaked units become useless, ruining the variety of the game. The Developer's Stance starcraft remastered maphack
So why do they do it?