every time you want to jailbreak your ps3. you will need to start it up with the jailbreaking device...in this case the ipod touch.
So its not just a do it once and works forever sorta thing.
But at least for the ipod touch. Once you jailbreak the ps3... you can unplug it from the ps3 and turn it off. It is only needed for the initial starting up of the ps3.
hope that answered your question