Once installed, you can drag any Office file into Chrome and it will open quickly, then you’ll be able to view it without formatting problems or changes. This is only a viewer, though. To edit your files, you need Microsoft Office, or can upload and convert them to Google Drive (which really doesn’t work well for Excel files).
As a document viewer, Chrome Office Viewer is actually really comfortable to use as you don’t have the big interfaces taking up space on your screen. The Google Chrome Blog also explains that opening a file in Chrome also protects you from malware that might be delivered by an Office document. The extension features a ‘sandbox’ that isolates files opened, so they cannot get wider access to your computer.