Juxtaposition is a technique that gets used quite often without anyone noticing. It gets used and misused daily by the media to great effect. To understand the power of juxtaposition I think it helps to talk about the Kuleshov Effect:
"Kuleshov edited together a short film in which a shot of the expressionless face of Tsarist matinee idol Ivan Mosjoukine was alternated with various other shots (a plate of soup, a girl in a coffin, a woman on a divan). The film was shown to an audience who believed that the expression on Mosjoukine's face was different each time he appeared, depending on whether he was "looking at" the plate of soup, the girl in the coffin, or the woman on the divan, showing an expression of hunger, grief or desire, respectively."
The mere act of putting two objects next to one another causes the brain to create a connection between them. This technique can be used to synthesize ideas that aren't actually represented in the frame.
It can even play a role in the daily rhythm of reading feeds. Just like film, feed readers are splicing together many different streams of information. In film, it's a series of images, and in feeds, it's a series of posts, but its the same principle. You benefit from the ability to organize your feeds into folders and then consume them as a group. That way, your brain can make connections between the posts. Luckily, feed readers are flexible enough to mix together streams like this, but it's only one form of flexibility.
Flexibility is the basic tenet of a feed reader. It lets us get more out of what we read, it makes us more efficient, it even lets us juxtapose posts as we see fit to help build a richer context. Interestingly, Google Reader was founded on this premise.
If you read some of the posts that Chris Wetherell wrote about the birth of Google Reader, you will find that he considered flexibility to be one of the foundational pieces of Reader.
"I believed a feed reader's interface might have to be athletically flexible to match a wide variety of reading styles." — Chris Wetherell
I don't think this is true of just the interface either. Feed readers are already flexible, but they could do so much more. Folders and labels are a great place to start, and, as we have seen, there are a great many feed readers that support this form of flexibility. But we could see more. Even if it's just so that we can support more people. Again, Wetherell:
"On this point I'm relying on data that is attainable at Google because of size and market dominance as well as having routine user studies and follow-up. So because of this data I'm making an assertion that there is something inherently different about the inflexibility of feed reading styles than compared with other software." - Chris Wetherell
If this has upheld over the years, it's possible that we haven't fully expressed all the different ways a feed reader could work. That means feed readers aren't as inclusive as they could be. There is even a bunch of low hanging fruit that hasn't been picked yet.
The hygiene of RSS feeds is lacking, but there is a lot of metadata that can be gleaned from feeds that doesn't seem to be widely used. For instance, authorship and tags. Why don't we see more feed readers sort information in this manner? Being able to read the most recent stories by Author X and the most recent stories tagged B seems like a great feature for a feed reader. If you built features using this sort of information, a feed reader could be even more flexible.
Hopefully, you can see a couple of reasons why flexibility is key for feed readers. The more ways you can put two stories next to each other, the better off you are. The more ways in which we can juxtapose two posts, the better off we are. These contrasts spark new ideas in the reader and create a more interesting context.