From Just Solve the File Format Problem
winstart.bat is a batch file that was executed before loading WIN.COM (Windows GUI) in Windows 95, Windows 98, and Windows ME operating systems (NOTE: Check if it was loading in prior versions!)
The intention of this file was to prepare memory and potentially start additional drivers needed by the user interface. A common strategy was to unload drivers, which could be unloaded, if they were not needed. A mouse driver, for example, was not needed for GUI, since it used its own.