Computer chess engines compute a factor for any given board position, which indicates which player’s in the lead and by how much. “1.5” would indicate that white is winning by about a pawn and a half, while “-3.0” would indicate that black is winning by a full minor piece.
If you plot the evolution of this factor over the course of an amateur’s game (like mine), you’ll usually see fairly dramatic shifts and changes. At one instance in the game, I could be up by two points, while one move later I’m suddenly down by three. (And depressingly, the amateur player usually is hardly aware of who’s ahead in these positions…)
The evolution of Grand Master games are usually characterized by a very tiny advantage attained by one player at the beginning, and then slowly and smoothly grown over the course of the game. For example, after the opening, white may be up by 0.4 points, and then 50 moves later have grown their lead to 2.5 points at which time black might resign. There are rarely the sudden changes you see in amateur games.