Generally the process oriented companies or the companies that has CMM certifications will conduct FCA/PCA for every milestone delivery that they make.
Now what is FCA?
FCA stands for Functional Configuration Audit. Here the functionality or the scope of your project is checked. Whether the project has adhered to all the required functionalities. The auditor may execute and verify few requirements on a sampling basis. They will also verify your traceability matrix to ensure that the requirements can be tracked at any point of time.
What is PCA?
PCA stands for Physical Configuration Audit. Here the physical artifacts like the design document, test plans, test results, etc will be verified by the auditor. They will check if they reflect the requirements or anything has been missed out. Another check the auditor makes is the time stamp check.
For example, the date of the design document should be less than the code's time stamp. If during the later stages of the project, the design document undergoes a change based on a requirement change by the customer then the design review document should also reflect a later date than the design document following which the code will be changed. This is to ensure that all the artifacts are updated with latest changes.