SSNL Theory Question: Controlling pot size?

[Kyriefurro]

In a previous post someone said that one of the mistakes that Limit players make when they move to No Limit is failure to control pot size. And I'm embarrassed to admit that I'm one of those players. I'm honestly not clear on this concept. So.....

1) What do meant by it?

2) How do you do it?

3) When does it apply?