Questions about betting impetus

[pergesu]

I was reading some archived posts, and read one of by Irie on the concept of betting impetus. Looked interesting, so I did a search and read a bunch more posts, but I still didn't really get an explanation.

Irie kept saying that impetus is crucial in determining how to play out a hand. A key point, he mentioned, is that you don't need to seize impetus in order to play a hand strongly. Sometimes you'll have impetus and want to surrender it. Other times your opponent will have impetus and you'll want to seize it. Yet other times he'll have impetus and you'll opt to let him maintain it.

The biggest thing that I'm missing to this point is why? Why do I want to seize impetus? Why do I want to surrender it? What situations do I need to look for, and what do I need to consider to use impetus as a weapon of my own?

He made a couple posts about this, and has mentioned it as a key skill that some of his backees have acquired. Seems to be pretty important and effective then, so I'd like to have a better understanding.