Q. Likewise some systems support many types of structures for a file's data while others simply support a stream of bytes. What are the merits in addition to demerits?
Answer: A merit of having the system support different file structures is that the support comes from the system individual applications aren't required to provide the support. In addition if the system offers the support for different file structures it can implement the support presumably more resourcefully than an application.
The demerits of having the system provide support for defined file types is that it raises the size of the system. In addition applications that may need different file types other than what is provided by the system may not be able to run on such systems.
A substitute strategy is for the operating system to define no support for file structures as well as instead treat all files as a series of bytes. This is the method taken by UNIX systems. The advantage of this method is that it simplifies the operating system support for file systems as the system no longer has to provide the structure for different file types.
In addition it allows applications to define file structures thus alleviating the situation where a system mayn't provide a file definition required for a specific application.