Keeping your knees touching the tank helps keep your weight from shifting around, which has some impact on the steering input you're feeding the bars. It's a good thing to do during normal riding, not just emergencies.
Need to know some of the smart things one could do with his hands in perilous situations.
A light grip on the bars. I think I use two fingers and a thumb. If the solution to the problem is continuing straight, or nearly so, two laws of physics come to the rescue. You and the bike are a large mass traveling in a straight line. One of Newton's laws states that this will continue unless acted on by another force. The second is the gyroscopic force of the spinning wheels. They want their axis (axles) staying just like they are. On loose gravel or steel decking your tires are constantly hunting sideways, falling off high spots. Feels terrible but forces are really low compared to the two that want to keep you straight. Easy for some of us to manhandle the bars into oscillation whereas doing nothing would achieve the desired results.
If turning is required, a good grip on the tank reduces the work of your arms from hanging on for dear life and steering to merely steering. Something about it tells me that whatever lean angle I need to push into the bars is OK. Works for me. Whenever I need to do it, I always think about those wonderful old Triumph tank pads on that skinny tank.
Its a pleasant surprise to learn this, because my natural riding instincts made me always knee-grab the tank while riding. So much so that i noticed some scratch marks on the tank due to the knee armour i often wore, mentioned in my previous post. http://www.st-owners.com/forums/show...ads&highlight=