Custom Formula Fields can be added to Reports and then are available within Dashboards too.

The benefit of Formula fields is that the underlying value is not stored within the database (so SF do not duplicate data) and the formula value is calculated when the user accesses the record (UI, Report, Related List etc....) Subject to FLS which each formula field has (just like a normal field).

Note that if a formula refers to 2 fields in SF and derives a computed value, the user does not need access to all the fields in the formula field, just the formula field.