When you click on a global resource, it automatically downloads. From a user perspective, they may just be checking out WHAT the document is and may find that it's not what they're looking for. Additionally, it seems that a lot of people miss that it automatically downloads and just think the link is broken.
+1 for this! PDFs will open in a new tab, allowing the learner to somewhat preview that type of file. But ideally, a file could preview in an i-frame/popup module, before prompting the learner to download if they want to.