Twitter is reportedly experimenting with a "mute" button, which would let you follow someone without seeing their posts in your feed.
The mute button is apparently just a test for now, appearing for at least a couple of people within Twitter's iPhone app. Twitter acknowledged last fall that it's been running more experiments, but there's no word on whether mute will launch for everyone.
Mute would be helpful for whenever someone you follow is getting too noisy. While you can always just unfollow that person, doing so would prevent you from exchanging direct messages, and may also just come off as rude, especially if it's a friend or family member. Some third-party apps, such as TweetDeck and Tweetbot, have their own mute buttons, but because those apps aren't available on every platform, there's no good way to mute someone across all your devices.
Last December, Twitter flirted with mute functionality by changing the way blocking worked, so that blocked users would still be able to view, reply and retweet whatever you wrote. The backlash was so strong that Twitter quickly reversed its policy. This only solidified the need for a separate mute button, so hopefully the feature will graduate from the lab soon.