Uses of User32.dll

Managing Windows
User32.dll contains a number of user interface functions involved in the implementation of program windows and their interactions with each other. It is responsible for implementing a GUI (Graphical User Interface) that corresponds to the look and feel of the operating system. Some of its operations involve in the creation and managing of windows, displaying text in a window, such as alert boxes and message boxes. It also deals directly with elements such as dialog boxes, your cursor, your keyboard, taskbar, even the exact coordinates of different windows on the desktop screen.
Major Time Saver
Software developers and programmers write software that use and interact with many different functions within User32.dll. Such functions help them to open and create dialog boxes for their applications; others help them store information to the Windows clipboard. Without the User32.dll file, programmers would have to write every piece of code for displaying their application windows on the screen, moving the windows across the screen, even the look and feel of their application to relating to the system's look and feel. That would take up too much time and resources. Thus proves the true purpose and effectiveness of the User32.dll and other similar files. With more than 700 different functions contained within User32.dll software, developers and programmers using that file have a lot of flexibility for extending the capabilities of their software.
High Level of Shareability
User32.dll, as with most DLL files, may be shared by Windows for performing many of the standard tasks you take for granted, including multitasking, showing and hiding of your taskbar and the movement of your cursor. Other software and applications as well can make use of features within the file for their programs; in fact, the file can be used and shared by multiple programs at the same time.