DLLs are useful for:
•Speeding up simulation time: When a diagram contains DLLs, it requires less disk space and memory since its executable program files contain the names of the DLL functions but not the code for the functions. For particularly large diagrams, the use of Embed-callable DLLs can significantly increase the speed of your simulations.
•Performing multi-rate execution: When a compound block is converted into a DLL, the DLL retains the step size and integration method in use at the time of DLL generation. If the diagram that calls the DLL has a faster or slower step rate, the DLL skips or adds steps to maintain its own clock rate. This allows you to have a low frequency overall diagram with high frequency components compiled as DLLs.
•Protecting intellectual property: Because DLLs cannot be reverse-engineered into readable source code, you can be sure that no one can access your intellectual property.
•Interface with other applications or simulators