I too was looking for examples of practical uses of RRDS VSAM files. Didn't find much on the net except for this PowerPoint presentation. (Note to Moderator: hopefully not any copyright issue? PPT is quite freely accessible in my google search).
It, basically, explains that the most appropriate use of an RRDS would be when there is an obvious relationship between your record key and your record's RRN. For example, if you are a telephone company that needs a customer file by telephone numbers. Or if you are a bank that needs customer files by SSN.
A randomizing algorithm would need to be used to avoid large areas of empty RRDS slots for the above cases. All very nicely explained in the above link.
Thought of adding it to this post in case other folks (like Abijoy and myself) are curious about this 'beast'.