I am evaluating the design of a system which will use FileNet to store documents and may use SharePoint as the front end.
What I am wondering is: Why not just store the documents in SharePoint? What is it that makes FileNet such a better system?
Most likely they already bought FileNet and decided on it as the standard for records management, but also seperately decided on SharePoint as the standard portal.
SharePoint is indeed capable of storing all sorts of files, and there are no technical reasons against using it, but enterprise architecture typically involves a lot more than purely technical reasons.
According to https://technet.microsoft.com/en-us/library/cc262787(v=office.16).aspx, Sharepoint 2016 supports up to 60 million items sizing 4TB in an actively used document collection, more if used in an archive type of system (low read/ access count) Older versions 2013-2010, etc. supported less.
SharePoint is useful as a collaborative tool for modifying word documents, excel sheets, etc. FileNet is more driven toward enterprise content management for large scale, and workflow based content processing and access.