Helping with homework: when does help become a hindrance?

I was an independent, motivated student and so my parents never felt the need to watch over me to make sure my school work was done. They trusted that I knew what I was doing and so long as I continued to prove them right, they left me alone. I understand that not every student is motivated or eager to do well. So parents often ask my advice about how much intervention is appropriate, and where/ how to draw the line when it comes to helping with school work. My answer is not the same for everyone.