This means, increased tension all the way on the leech -- limiting its freedom with wind. Not letting it twist on the top -- where the wind is high -- quite as much for instance. This also means the wind at the top would behave similarly to the rest of the sail.

The foot has decreased tension which means it can inflate to port (if on-starboard), or starboard (if on-port).

"Putting more tension on the foot, easing out the leech."

"leech would twist out and away downwind". Especially at the top.