How long can you keep doing laser treatments for acne scars?

So, I’ve been doing fractional CO2 laser treatments for my acne scars and have completed several sessions so far. While I’m still seeing improvements, I’ve noticed that the results from the most recent sessions aren’t as dramatic as the earlier ones. I’ve heard about the plateau effect with lasers and I’m wondering:

1.  How long is it generally safe to keep doing laser treatments?
2.  Is there a point where laser treatments stop being effective?
3.  Are there any risks of overdoing it?