RPF CHECK DOUBT!!!

Can sumone xplain me clearly about rpf check and its diadvantages???
I have read and confused a bit
here is wat i have understood
If a router running multicast recieves a multicast packet from an interface
and that local router checks in its routing table tat the interface which it
has received the packet is the best one to reach tat particular source.
Even if there are two or ore interfaces where we can reach it ,but the one
in which we have received is the best interface
If this check passes,then the multicast operation starts working...

Am i right with the concept???

pls anyone expalin me in depth!!!!!!!!!!!!

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