Occasionally, when you are not trying to move about the cabin and no one is trying to squeeze past you, you may have the luxury of placing your feet wide apart and hanging on to something not in line with your feet. Most of the time, though, your feet will be too close together, or inconveniently aligned, or alternately off the deck as you walk. Practically, you can count on our feet only as a single point of support.
Now, you will want at least one hand available to comfort and assist your passengers (otherwise you might as well remain belted into your jump seat), leaving you one hand to hold onto the airplane. This provides exactly one more point of support. Turbulence is quite random and you might get a push in any direction. Unless your wrist is exceedingly strong, you can easily be spun around the axis through your two support points.
By holding onto the overhead track you can greatly reduce the leverage operating to spin you around by keeping your center of mass very close to your support axis. Holding onto a seat back or other low handle moves your center farther from your support axis greatly increases that leverage.
When turbulence moves the cabin vertically, you can be lifted right off the deck, and you may not come back down where you were. If you press upward on the overhead track you can easily apply enough downward force to keep your feet in place. Of course you have to be prepared and react quickly, but this will come with experience.
If you have a good grip on a seat back or seat arm, and the aircraft drops suddenly, you might even be pitched over your handhold and onto the seats. Of course the entertainment value of an upended cabin attendant will temporarily distract the passengers from their trepidation and discomfort, but as with all slapstick comedy, the risk of injury is great if it is attempted without training and practice.