There can be reasons why users would want to be able to update the records they are seeing in the report. There could be a known error that users are aware of in their accounting system that is producing the wrong Journal Entries that they are seeing, long term solution will be to correct the data from the system, but for auditing purposes at quarter-end, they are just going to manually update the record through OBIEE report so that the numbers will balance out.
Another user case can be to have users manually update their username and password in OBIEE on their own. I know that in big enterprises, the user credentials are typically synchronized with their other credentials so it would not likely to have such requirement to let users change their passwords, but in some cases where you may have external users who are not part of the company, they may want to have their own password that can be changed. They can do so by using writeback against the user table to have username and password fields updated.
Anyways, the set up of writeback is pretty standard, which I am not going to get in too much details. Google around and you will find many articles that shows you how to do so. Basically, it comes down to the following steps:
1.you update the instanceconfig.xml file to enable writeback feature.
2. Enable writeback on the columns you want in rpd (BMM Layer)
3. Give permissions to the application roles to have writeback, done in RPD. (Check permission identity manager and presentation column)
4. Create writeback template and save it as writeback.xml file and put it in following directory in the obiee server machine /opt/app/OBIEE/instances/instance1/bifoundation/OracleBIPresentationServicesComponent/coreapplication_obips1/analyticsRes/customMessages/