Not being an nhl analyst cannot give you the exact answer, but you would use things such as time ice, Shift length, when during the game. The score at that point, the number of battles/hits/takeaway/meters covered etc
in one game it might not be obvious but over a season you could easily gain some trend analysis.
this would be able to tell you for a player how they performed at different stages of a game - do they alway seem to float around when going down a goal, or can you see an increase in meters covered, battles undertaken in shifts after a goal etc