Calculated fields are a powerful addition; they can be used in many scenarios, some of which are:

• Number calculations, (for accounting, weights, and so on)
• Retrieving values from related entities
• Constructing a string based on other attributes

The TechNet article (https://technet.microsoft.com/library/dn832103.aspx) covers calculated fields in a few examples. The article also covers some limitations of calculated fields. Among them are the following:

• Calculated fields cannot trigger a plugin or workflows
• Once a field is created as simple, you cannot convert it to a calculated field without deleting it; (something to consider when upgrading old versions)
• A calculated field cannot reference itself, but it can reference another calculated field or rollup field (limit of five chained fields)
• Values in the calculated formula can come from the current entity or a direct parent (no access to 1:N or N:N entities)
• Up to 10 unique calculated fields can be used in saved queries, charts, and visualizations
• You cannot define a maximum or minimum metadata property on a calculated field

At the time of writing, in addition to basic arithmetic operations, the Dynamics 365 supports the following built-in formulas with their respective return types: