The short answer is: it depends completely on the type of usage of your music. For placements in movies, commercials, and TV, the payments for sync licensing will typically be larger, but they are different for every project. When your music is added to videos on YouTube, you'll make money from the ad revenue generated on those videos. Ad revenue payments will also vary for videos where YouTube has identified your music in the content ID process.
Like everything in the business, there are few accurate ways to gauge success in advance. But remember, it costs nothing to opt in. Sync licensing is a great way to get your music working for you, so it’s added revenue that you probably weren’t seeing before.