why - To allow customers to send logs for production LBs to one end point and non-prod LBs to another. Many customers are probably using namespaces to segregate environments and product lines, in both cases they might want to ship logs to different locations based on product line or environment. There is also a security aspect to this. Generally its best to not mix production logs with non-prod logs. Today that is not possible unless a separate tenant is used for non-prod but that is not a good solution because its common to have policies shared between prod and non-prod LBs.

who - Security or routing engineers.

how - have a drop down list, multi select in the GLR config that allows selecting one, many or all namespaces. or excluding one or many namespaces.