When a tweet is imported into an outside app, it will look more like how it appears on Twitter’s app and website rather than a static screenshot. On Snapchat, the tweet will also link to the original (Twitter says it may add similar linking functionality to the Instagram version as well).
Using Twitter’s share menu might not look all that different than just posting a screenshot, but it might be more convenient than cluttering your Camera Roll with unnecessary screenshots. And for Twitter, it gives the company a chance to take some more credit for some of its most popular content.
Funny tweets have spread widely across Instagram meme accounts and other apps, but these screenshots do nothing to bring people back to Twitter. And inconsistent cropping can make them jerky and hard to read. By giving users a way to neatly share tweets with other apps, Twitter will at least ensure that its content looks good when it goes viral, even if it isn’t in its own app.