The benefits of using CMIS might be quite clear to you now, but let's walk through some of them:
Language neutral: Any language can be used to access a CMS system that implements the CMIS service interface, as long as the language has the functionality for making HTTP requests and can handle XML or JSON. So you could have a C++ application accessing a content management system written in PHP.
Platform independence: It doesn't matter what platform the CMS system is implemented on top of. As long as it supports the CMIS standard any client application can talk to it if it has the capability to make HTTP calls and parse XML or JSON.
Standard service API: Clients need to use only one API to access content management systems and they have a much better chance of not being limited to only one vendor's API and platform. This is probably a great benefit as it means that you can work with any CMS system after you learn to work with the first one, thus saving time and money. It will also be easier to find people who can work on new CMS projects.
Standard and easy-to-learn query language: The CMIS query language is easy to learn and adopt as it is based on the ANSI SQL-92 standard. So you can use SQL syntax such as
SELECT * FROM cmis:document WHERE cmis:name LIKE '*alfresco*';.One application to access them all: End users can now use one application and user interface to access all content management systems, and do not have to learn about a new user interface for each and every CMS system that the organization has deployed.
Easy workflow integration: It is now much easier for a company to deploy an enterprise workflow that interacts with content managed by multiple content management systems.
Repository vendors get more applications: CMS vendors are more likely to get many more client applications using their server as any application that uses the CMIS API can access any CMIS repository.
Applications get a bigger customer base: Applications that are written to support the CMIS interface are more likely to get a bigger customer base as they will work with a multitude of CMIS-compliant content management systems.