No. Soundiiz is doing a copy process (as much as possible with a matching system) from your source platform to the destination.
That means we are looking at your source playlists and favorites lists, reading metadatas like the title of the track, the artist and trying to found a similar element on the destination catalog.
So, your source playlists and favorites will not be deleted during a convert or a Platform to Platform process.
Be aware that if you are using any "delete" button on Soundiiz, that will also delete instantly on the music service too, so be careful when deleting an element on Soundiiz.