When you are viewing an article in the Embedded or QuickView viewers you can quickly zoom the page to fit the available screen size using an action on the overflow menu. With some feeds you will find yourself always performing the same page zoom before reading the article. In this case you may wish to set the feed to automatically zoom the page once it has finished loading.
This may sound like a great time-saver, but note that it brings a potentially negative side effect with it. The autozoom will only be performed after the page has completely finished loading. If the page loads slowly you may be tempted to start reading it before it is completely downloaded, but if you do, once the page load is finished and the autozoom executes the page will suddenly resize and jump back to the top, regardless of how far down the page you have already read. For this reason you may choose not to use autozoom, and instead just use the overflow menu zoom actions once enough of the page has loaded to start reading it.
If you do decide to use autozoom, you can set it at the global settings level, and also override the global setting for each feed/aggregate. Autozoom can be set to zoom the page to fit the screen horizontally, vertically, or both.