Say you have a scene, fragment, or a full manuscript that involves some sciency events, and you need to make sure all of them are correct or at least make sense within the context of your fictional universe before your work is ready for publication. You don’t mind making the corrections yourself, or doing the required research on your own, you just need someone else to point any errors or inconsistencies out to you so you can fix them. This is, essentially, what a science review is: almost like a proofread, but specifically for the STEM-related aspects of your manuscript.