from Kevin Woodley at NHL.com,
In the simplest terms, narrowing the stance improves a goalie's mobility by keeping his feet underneath him and giving him more leg extension with which to push. Conversely, if a goalie is already spread out too wide with his legs, there isn't much extension left to make a powerful, controlled push, whether it's left to right or up and down the crease.
"It's just easier to move," said Detroit Red Wings goalie Jimmy Howard, who has a .915 save percentage in 2 1/2 seasons since making a similar stance adjustment after 2015-16, when he had a .906 save percentage. "You are just freer to move. With better hip mobility, you can hinge better, and that way you can get better pushes. I still get wide when the puck is below the hash marks, just to give yourself a little more blocking surface but also to get down into that butterfly a little quicker, but I used to be wide all over the ice."
Howard, who played in the 2019 Honda NHL All-Star Game at SAP Center in San Jose, also adjusted his positioning with new goaltending coach Jeff Salajko after the 2015-16 season, playing within his crease after being one of the most aggressive goalies in the NHL early in his career. But narrowing the stance was the biggest change for the 34-year-old.
"Getting older, it's a lot easier on your body, that's for sure," Howard said.
more with other goaltenders dicussing their style...