When LDPoRSVP is required? In which case it is a requirement to tun LDP over RSVP?

there are few secnarios where we can use LDPORSVP 

CASE 1. WHEN WE HAVE TO MAKE OUR CORE LDP FREE AND RUN LDP OVER THE EDGE ROUTERS ONLY . 

THE benifits we get is scalability and fast failover for any kind of issue between the p routers .

Case 2 

 WE can use the same for TE TUNNELLING WHEN WE ARE RUNNING OSPF AS IGP INSIDE THE ISP CORE. AS WE KNOW VERY WELL OPAQUE LSA never leave there area i.e we have to run a single area inside the core to make our TE work fine but it has its own challenges like scalability , convergence etc.  so we need to run multiple areas which are connected to area 0 but to make our te work fine we have to run LDPoRSVP  between the devices . 

https://www.juniper.net/documentation/en_US/junos/topics/example/vpn-ldp-over-rsvp-topology-configuring.html

FYI.