Formatters were applied to every content item before. Different content items made from the same source items would cause the formatter to run once for every item, even though the output would be the same for the same input. The new release fixes this and caches the results, to be reused if some content appears on another page. It shouldn’t cause any problems, but if it does, it can be disabled.
It is more or less a beta release. All essential features are implemented and working (as far as I know), and I don’t think there will be a lot of incompatible changes in future releases. The next release(s) will focus on improving the performance, which — at the moment — sucks.
Check out this great example of a blog generated by Newcomen. ☺