Summary

Custom assemblies greatly expand functionality (as compared to expressions and embedded code) that can be accessed from a report. A custom assembly can be written in any .NET language. Custom assemblies can leverage a full set of productivity enhancements available in Visual Studio .NET, such as Intellisense, source code management, full debugging capabilities, and much more.

Custom assemblies can be used for complex code, where usage of expressions and embedded code is no longer elegant. If a custom assembly requires more than default Execute permission, you need to have a good understanding of .NET security and SSRS configuration, modify configuration files to set assembly's permissions, and assert the permissions in the assembly's code.