When associating objects with each other, there are two main choices: Lookup fields vs Master-Details fields.
Here are some considerations for these two:
Master-Detail fields
These fields create a strong connection between two objects. The field is created on the “detail” object, and points to the “master” object. (Note: The word “master” can be sensitive to some, and some platforms call this a “parent-child” relationship instead).
A child record always has one, and only one, parent. The parent record must be created first, and then the children can be created. If the parent is deleted, all related children are automatically deleted. This is called a cascading delete.
Further, due to the strong dependency, you can create roll-up summary fields on the parent that obtain the count, sum, min, and max of an attribute of their children.
Lookup fields
These fields create a loose connection between two objects. Records can exist with or without a lookup relationship in place. Records do not cascade delete.
While roll-up summary fields are not available out-of-the-box, you can install a popular app called Declarative Lookup Rollup Summaries (DLRS) to assist you. This app is so popular it’s available on Salesforce’s installation page for nonprofits.
The takeaway
It’s generally advisable to create Lookup relationships instead of Master-Detail ones. You can even set the Lookup field to be required, which then operates very closely to a Master-Detail field.
With DRLS, you have incredible power creating roll-up fields using either type of field.