The Midgar Zolom save glitch refers to a trick in Final Fantasy VII that allows the player cross the marshes without encountering the Midgar Zolom. Once on the marsh, the Midgar Zolom's shadow advances upon the player and triggers a battle when it reaches them, making the marshes difficult to cross without a Chocobo. However, if one saves the game before the shadow reaches the player, then exits and reloads, the player will be in the same position but the Zolom will spawn on the other side of the marsh, giving the player time to make it across.
The Midgar Zolom's spawn setup is to prevent the player being trapped in a cycle of battles, and give time to escape the marshes. While its position being reset does prevent a save file being forced into an unavoidable encounter, being able to save the player's position in the marshes at all is a programming oversight.