It defeats your purpose for being here, namely, to learn.
Cheating is unfair. It penalizes honest students whose grades reflect their best efforts and who may not get the grades they deserve because others are cheating.
It can ruin your relationship with your professor.
You are part of an intellectual community to whom you owe an obligation of academic integrity.
It is counterproductive. If you cheat on assignments, you won’t learn the material you need to know for prelims or finals or possibly graduate school or professional life.
Taking someone’s work or using their ideas or words without acknowledgment is no different from stealing.
You risk losing respect and even self-respect.
Once you start cheating, it can become a habit and difficult to stop.
Even if you are not caught, you are likely to regret cheating.
It’s not worth the risk. If you are caught, the consequences can be severe.