Facebook changes are always notable if only for one thing, no matter how great or small, there are people who are going to hate them and they're not going to be quiet about it. The latest minor change: the News Feed font is now smaller. It's not a huge difference, but people are already complaining about it."[W]hat happened to Facebook? posts' and status' font size is too small to see! even the most catchy post becomes UN-NOTICE [sic.]," one Twitter user writes.
While some are taking to Twitter just to point out that the font has changed, many are complaining that it is too small.
In all fairness, the new font is going to pose a problem for people with poor eyesight. Considering that screen sizes are getting bigger and resolutions higher, it means that on some monitors the new font is going to be somewhat harder to read.
Since the News Feed is at the core of all interactions on Facebook and likely the thing most people read on the site on a regular basis, this may pose a problem. That said, the changes are not that big that this is going to affect a lot of people.
As for why Facebook would do this, the most plausible explanation is that it wants to fit more content in the News Feed and one way of doing this is by making the text smaller.
Of course, Facebook may just be testing the new font size and may decide to revert it, or settle on a slightly bigger font.
The company doesn't make it a habit to listening to its vocal critics and prefers to launch new features and changes that it believes are beneficial and then wait for the users to adjust.
With over 500 million users, there are people who are going to hate anything that Facebook does and trying to please everyone is not going to enable the site to move forward.
UPDATE: You can check out a short tutorial on how to bring back the old font here.