Here are few paragraphs from the book,

Windows 98 also offered up full support for DOS applications because it can easily be switched to DOS mode. In doing this, DOS based applications can handle the system in their native environment. Having DOS mode available also provides for easier ways to fix system errors without having to enter into the graphical user interface.

Like other previous versions of Windows, this operating system wasn’t without its problems. Windows 98 was never as stable as common users had hoped. Often, the software developers of drivers and applications had insufficient experience with the creation of programs for this new system. This caused many errors generally described as system errors by users even if the error was not caused by parts of Windows or DOS.