I wouldn't call rushing a good or bad tactic. It's like any other tactic, it has it's flaws and it's benefits.
You might catch an opponent off-guard, especially if they've gone for cash-grab tactics (gather resources as fast as possible), rather than a more rounded defensive approach, but then again if they repel your rush there's a good chance you've been neglecting your base too, and a counter-attack has a high chance of devastating you.
You might catch an opponent off-guard, especially if they've gone for cash-grab tactics (gather resources as fast as possible), rather than a more rounded defensive approach, but then again if they repel your rush there's a good chance you've been neglecting your base too, and a counter-attack has a high chance of devastating you.