Trimming the ODI repository makes the repository more responsive and enables quicker patching.
Trimming content is not suggested as a best practice after deployment. This is just guidance if you are experiencing issues (such as ODI export/import taking long time) due to the large size of the ODI repository. For instructions to trim the ODI repository, refer to My Oracle Support Note 1970123.1 - Trimming BI Apps ODI Repository.