What is the difference between direct arithmetic computation and using MegaWizard blo

Thanks very much. But why I ask this one in Altera Mysupport, I got the following answer, which causes me confused again:

I answer your question as below.

The Altera® integer arithmetic MegaWizard offer user the convenience of performing mathematical operations on FPGAs through parameterizable functions that are optimized for Altera device architectures.

These functions offer efficient logic synthesis and device implementation.

User can customize the megafunctions by configuring various parameters to accommodate the needs.

Altera always recommend user using the MegaWizard in order to have the optimized synthesis result.