Multicast PIM Dense Mode

Hi,
thanks Laz , very well accepted solution
may i ask another question ?
because when you enter in multicast, you have some basic questions before you dive deeper in multicast
For exemple, when a lesson introduce dense mode versus sparse mode, you learn that a router designed in dense mode forward the multicast packets on all its interfaces (although this behavior is restricted by split horizon and RPF)
So, in this case, the first question that is triggering is: why do we need a multicast routing protocol in dense mode ? is it just for prune messages ? is it because in the real world , dense mode cannot exist without sparse mode ?
Thanks
Regards