At my organization we often want to approve copy that lives within Google Docs and slides that live in Google Slides. Currently, you can "attach" the Google files to a project or folder but you cannot attach them to a review/approval. For a marketing team that typically reviews copy and then creative within a single Wrike workflow (which has been AMAZING for other types of documents), this is a real hang up.
I do not need to be able to provide feedback via the native Wrike tools as Google has a great commenting feature already, but without being able to attach the files it makes it difficult to keep our projects within the proper workflow stage and for reviewers to know what they're actually reviewing. Other users have also posted about an integration like the one for Adobe CC—I feel that's likely not necessary, but I would take that over no functionality at all.
In its current state, being able to attach Google Drive files seems to be a nice to have for easy access but is at odds with how nearly every other type of file is processed and used for reviews.