It is possible to get Jenkins to either (a) keep workspace contents (yes, all the contents) and manage them consistently with the build retention policy
or (b) copy the workspace contents from a job to somewhere on the node where the job is running?
Generally, workspaces are transient, but sometime complicated build processes need to be able to review the workspace contents to debug conditions in the build environment itself. Keep a copy of the workspace might help.
I know other CI tools allow you to manage workspace as well as build and artifact retention.