There are community challenges in the game that alter the course of the galactic campaigns. Cheaters can swing challenges to victory which then means there can be planets you might never fight on because it requires losing a community challenge.

The devs have also said they want to tell stories using community challenges, so cheating can also hamper their storytelling.

Something not mentioned by others, you can't engage on completed worlds. If a world is lost or won it becomes locked out until it gets attacked again by either side (not automatic or guaranteed). Cheaters could potentially remove all content from the game.

It wouldn't effect you personally, it would effect the games overall progress. The way the game progresses for all players is effected by what planets are liberated and what missions are accomplished. All players are on the same team, meaning if some players cheat, it will significantly effect the outcome of these in game events.