The previous Chrome version, 2.0.1.0, only performed downloads with the browser. This only allowed simple downloads (1 URL to 1 file) and in many cases, the download would fail because the server verifies some meta information (like the "referrer" HTTP header) that cannot be faked with browser downloads.
The latest 7.3.3.2 version still permits browser downloads for compatibility, but also offers companion app downloads which allows faking referrers and cookies for simple downloads, but also permits downloading videos streamed using HLS and DASH protocols.
In fact, there is no real benefit using browser downloads.
With coapp downloads, there is no history saved anywhere, so when you close the browser, there is no trace of your previous downloads.