This alters the feed so you only see the latest tweet in a conversation. You can still click the tweet to toggle the conversation.
A lot of people have complained about the latest update to twitters web app with the way conversations are now displayed. This extension does one thing only, it hides all tweets in a conversation, except the last one, so your tweet feed isn't cluttered with multiple copies of the same tweet. Tweets that are part of a conversation still has the line above it, indicating it's status as part of a conversation, so they're easy to find if you want to click it and toggle the conversation view.