The MongoDB blog discusses how to create properties in a schema that are dependent on other properties, which allows for more sophisticated validation and data modeling. Property dependencies state that if one property is present, others must also be present, while schema dependencies define changes to the schema based on the presence of another property. The blog provides examples of both types of dependencies and demonstrates how they can be used to enforce complex validation rules in MongoDB. Additionally, it mentions MongoDB Stitch's validate expression feature, which allows for more advanced validation using Stitch functions.