If you are putting on a practice green in a room, you’ll likely start with the ball on the mat. This let’s you putt without any abrupt changes in the roll of the ball. There is little uncertainty other than your own execution. This is where most people are comfortable.
What if you pull the ball off the mat? Neglecting that you are now putting from further away, there is also usually a 1/2″ lip of mat material that is going to give the ball a more irregular bounce as it hits it. It introduces extra uncertainty that is much more difficult to compensate for. In fact, it’s possible that executing exactly the same every time and due to nothing but the uncertainty introduced results in a much bigger variation in results than executing the exact same every time will on the mat.
The question is, should you practice this putting off the mat or is it a waste?
On one hand, if the point is learning to put on the green, there should never be this abrupt uncertainty on the golf course. Of course, there is also times you may want to put from the fairway or the fringe and then this uncertainty is there again.
At a higher level of philosophical outlook, there is also the factor that while most of life is continuous and smooth, each day mostly like the previous, there can be uncertain “bounces”. No one is expecting it when their child gets sick and needs to stay home. No one expects a car problem like a flat tire or blown head gasket. No one expected a pandemic to shift the world of work so much for nearly every office worker. This isn’t even close to the full spectrum of “bounces” out there.
With this in mind, the answer seems obvious to me. Getting good at judging the uncertainty that can be introduced is a skill and should be practiced as much as possible.
P.S. Here’s a video of me putting from behind a mat to see the bounce. Maybe with practice I’ll get good at this, not just in golf, but in life.