My 3 month old is exclusively BF, I started off just rinsing nappies in the machine. It worked fine and the nappies and machine seemed fine. But then we moved house and I'm using a different machine now and I find I have to rinse the poo nappies before washing or they don't come out fresh enough. And the machine was a bit stinky

Now I rinse all poo nappies before putting the in the bucket, and do a rinse cycle before washing. So I think it depends on your machine , basically

If you do put the nappies straight into the machine, I think its recommended that you do hot wash with no load and full powder every now and again.