At Soundstripe, the majority of your music will be used for micro-licensing placements (indie films, youtube, wedding videos, ect). Most of the time, micro-licensing doesn’t generate a whole lot of performance royalties (aka residual income). HOWEVER, every so often we do deal with placements that generate performance royalties, and if you are not registered with a PRO (Performing Rights Organizations), you won’t see any of the royalties!
If your music is used for a "larger" placement such as a commercial, tv show, movie, etc, PROs collect money from the networks or companies that are broadcasting that content and pay you performance royalties. The only way to collect these payments is to register yourself as a writer and/or publisher with ASCAP or BMI (or SESAC, or whatever PRO is used for your country) and register your songs!