Tension and relaxiation durring ballistic drills

I could use some help with this because I am having a hard time mentally grasping exactly what the ideal mesh of tension and relation is during a swing. Keeping in mind that we are suppose to be using only as much tension as we have to.

1. Durring the entire swing are we tensing our stomachs? I have heard this several times but what is the reason for tensing the stomach mid swing? Is it not better to tense at the bottom and top?

2. At the top we are just making sure everything is tight, right? Am I correct in saying that we should not be squeezing too hard for that second long lock out.