A traditional publisher usually only publishes work for free. They do fantastic marketing, add you to all of the necessary wholesalers, provide ISBNs and set up events. Pretty much exactly as Hybrid publishing works. The main differences are:
Royalties are low, the standard rate is between 5-15% of the net price. Hybrid is generally 15 or higher (side note – our hybrid published authors get 80% book royalties – our traditionally published authors get 50% – you don’t need to print that anywhere – I’m just letting you know). You also get far less control in traditional publishing; your cover is made by the publishers without any huge direction from the author.