KML is an open XML format for geographic data, KMZ is its compressed variant (ZIP archive). They're essentially the same format with different properties.
| Criteria | KML | KMZ |
|---|---|---|
| File size | Large | Compact (ZIP) |
| Human-readable | ✓ | ✗ |
| Embedded resources | ✗ | ✓ |
| Google Earth | ✓ | ✓ |
| Easy sharing | ✗ | ✓ |
When you need to edit XML manually, debug geocoding, or integrate into code.
For email sharing, Google Earth publishing, compact storage.