Snapping the left leg straight near impact brings a whole host of issues into not only the swing itself but also can cause injury. John Daly (above) never had to snap or extend his left leg in an effort to create power- such as other long drivers are prone to do.
One of my PGA Tour players- Harold Varner III has a unique movement with his right foot into his follow through. HV is not aware of it and is never trying to do it. It's a result of something I explain in this video- and it may well help you.
Tighter circles of motion create faster movement. Learn how you can maintain the swing arc better to help create more speed and much greater control
Never try keep the head in the same spot- it can and will move based on how well we use the ground and turn our body. Find out more in this video
A full release asks for the entire rear side to drive and move with the release. Using the ground correctly in the downswing can help lead you to this added benefit of power and control.