With DokDok enabled on your Gmail account, every message will have a small box at the bottom where you can track attachments. Even if the message you're looking at doesn't have any attachments of its own, you'll still have the option to view your entire attachment history with the sender. Where it says ‘Latest files exchanged with", click the person's e-mail address to call up a list of file attachments you've sent to or received from them.
The attachment history list will give you the option to either open the original e-mail for each attachment or launch a preview of the attachment in a new tab. DokDok can surface every version of a given file that you've exchanged with your contact, and compare multiple versions to identify what's changed between them.
In my line of work, the differences between two different can be massive or subtle, depending on how far along a given project may be, so it's great to have a quick way to view revision histories without necessarily having to open a document.
For sales people in the field, who frequently repurpose the same slide deck in a variety of iterations for different clients, DokDok can offer a huge time savings. You can pull up the history of files you've exchanged with a sales assistant back at the office, and compare them quickly to select the one best suited to your next meeting without having to open each of them in turn.
DokDok can also save time when you're trying to recall past attachments you've exchanged with a given contact. Rather than wasting time searching for a past e-mail that contained an important attachment, you can just find the latest e-mail from that person, pull your attachment history with them, and select the one you need in a second.