When during movement does Guardian Of Faith deal damage?

The Guardian of Faith spell states something like…

A Large spectral guardian appears and hovers for the duration in an unoccupied space of your choice that you can see within range. The guardian occupies that space and is indistinct except for a gleaming sword and shield emblazoned with the symbol of your deity.

Any creature hostile to you that moves to a space within 10 feet of the guardian must succeed on a Dexterity saving throw. The creature takes 20 radiant damage on a failed save, or half as much damage on a successful one. The guardian vanishes when it has dealt a total of 60 damage.

Is this assumed that as soon as a creature stops in one of the squares around the guardian, it instantly takes the damage (less the saving throw)? E.g. in some combat situations…

• Creature ends its movement within range, will take damage.
• Creature moves through the Guardian’s range but does not stop, no damage

Am I understanding this spell properly? Seems like it would only really be useful to place in difficult terrain, or at some sort of objective point where the party actually has to stop for a moment (e.g. to unlock a door, climb, etc).