ETL Developer Sandbox in PROD

Database
Enthusiast

ETL Developer Sandbox in PROD

I wanted to get some input from some of the DBAs on this forum.  I have some ETL developers that want me to grant them some perm space in their database in order to create a personal sandbox for various reasons.  My guy instinct is to NOT grant this type of a sandbox as (1) it creates unpredictable workloads and (2) there is no design overview to prevent some really bad design decisions that could affect REAL production workloads.  I have other reasons for why I believe this is a bad idea but want to get some input first.  I understand the concept of a business Sandbox but have never been asked to grant developers sandboxes in a prod environment.  Does anybody else have any experience with this, and if so, how is it working.

Thank you,

Joe