A Solid Stance will give added consistency to your putting stroke. Take a look at the red squiggle in the centre of the image, see the way the it moves about ?. The squiggle shows the movement of the centre of gravity through the putting stroke. Having your body weight moving from right to left ( or left to right ) during the putting stroke will make putterface alignment and distance control variable. (The numbers in the corner show the distribution of body weight between left and right foot and from toes to heels. )  Take a look at your own leg action on your putting stroke, your knee movement should be at a minimum.

Now look at the image on the left, - a wider stance giving more stability and the centre of gravity is rock solid, a definite plus for the putting stroke.

 

To go with a wider stance try firming up your legs by feeling like you are pressing your weight into the floor through your legs.