From the website:
This service allows you to connect a Mastodon account and a Twitter account and enable cross-posting between them. You can choose some options, such as if you want to post boosts, unlisted toots or replies.
I recently convinced my wife to give Mastodon a try and helped her setup this service to automatically crosspost everything she publishes on Mastodon to her Twitter account. It works like a charm.
Now she can publish to Mastodon without leaving everyone on Twitter out of the loop. But if you’d prefer to publish to Twitter and crosspost to a Mastodon account, it can be configured to do that too.
I suppose this is a roundabout way of nudging all of the fine folks that created a Mastodon account, but abandoned it to head back to Twitter, to setup crossposting and keep one foot on each side of the fence. I think it’s pretty forward thinking to at least maintain a presence outside of the current big social networks.