Sync could simply be explained as the process of making everything the same in multiple places. In terms of an RSS reader, I think it’s the technical cornerstone of the tool. Information doesn’t care where you are or what device you are on. It is created at breakneck speeds, and you should be able to manage it from anywhere on any device. While this is a clear value proposition, not everyone would agree, but there are other reasons why sync is important.
Until the world has an ansible, information will take time to travel, and any means of connectedness can falter for any number of reasons: trains, planes, or living in a place with crappy mobile service are all ways in which many of us experience unreliable Internet connectivity. One way to combat this is to make sure there is a way to sync all unread posts. Many readers already do this, but not all. One reason they don’t — and I don’t think it’s a bad one — is that downloading all of your unread items is slow. That’s true if you are just grazing for information. But is that what you want to do when using a feed reader? You have to answer that yourself if you are making a feed reader, but I, your opinionated author, would argue that you should just do offline as a start, and do any other sync as an additional improvement.
Another reason to make sure that all unread stories are downloaded is context. I want to know where I am in my unread items. I don’t need to know the number, although that would be nice. What I need to know is how close to the end I am. That scroll bar on the right-hand side of the screen shows you where you are in relation to the end of the feed. When things get globbed on to the bottom as you go, you don’t ever really know how far down the feed you are. If you had all your items on your current device, you would know where you were.
Importantly, I don’t think one type of sync precludes another. Having a well-built backend would make it possible to do any kind of sync. Also, when considering the flexibility needed when creating a feed reader, this might be one of those things that you should be able to do in whatever ways makes sense. By making sure there is choice for the consumer, you can satisfy a wide array of reading habits. Yes, this is another reason for there to be many reading UIs connected to one platform.
Thanks to Jon Mitchell (@ablaze) for editing this post. He just started on amazing new journey at The Daily Portal if you are interested in new ways of publishing online you should check out his site.