Keys on when to rotate as lead

[zebraman]

I have heard many different keys on when to rotate as lead. I was just curious to get input from others on what they have heard. Here are the ones I can remember.

1) "When the ball and more than 1 matchup is on the C's side, go"

2) "When the ball and a post player are on the C's side, go"

3) "When the ball penetrates past the foul line extended on the C's side." (I've heard this one a lot and it's way too late in my opinion)

and my favorite (and the one I use because of it's simplicity),

4) "go when the center needs your help."

What are some other keys that you have heard or that you use?