Complex sentence: The same flexibility that permits an upgraded library to benefit all dynamically-linked applications can also lead to DLL hell; if every application on a system must have its own copy of a dynamic library to ensure correct operation, the benefits are moot.
Split into simpler sentences: The same flexibility that permits an upgraded library to benefit all dynamically-linked applications can also lead to DLL hell. If every application on a system must have its own copy of a dynamic library to ensure correct operation, the benefits are moot.