The IEEE 830 standard defines the benefits of a good SRS:
A Complete description of the software's purpose and functionality.
Details as to how the software will perform in terms of speed, response time, availability, portability, maintainability, recovery speed and more
Use cases of how users will use the software
The definition of how the application with interact with other hardware and program
Non-functional requirements (e.g: performance engineering requirements, quality standards, or design constraints)
Save time on communication
Minimize development efforts
Gives the customer feedback
Eliminate task duplication
Facilitate the transfer to new users or to new machines
Breaks problems down into parts
Serves as the main document to verify the validation and testing processes
Referring to past SRS documents helps identify deficiencies and process flaws.