Hi Michael,
In this example R1 originates the prefix so the next hop is 192.168.12.1.
R2 will reflect this prefix to R3 but it doesn’t change the next hop. Using next-hop self on R1 won’t help here since 192.168.12.1 is already the next hop IP address.
The route reflector will reduce the number of iBGP peerings but that’s it 
About your question, let’s imagine that R1 learns 1.1.1.1/32 from an eBGP router. In this case, it would be better to make R1 the RR and use “next hop self” for all other iBGP routers. That would ensure that all iBGP neighbors learn the prefix and are able to reach it.
Rene