Since RSVP can distribute label, in network scenario where implementing only MPLS TE and VPNl3 and every PE have fullmesh MBGP, I don't need to enable LDP to make it works.
What is the advantage on top of RSVP if we have to enable LDP?
You are correct. You do not need to enable LDP in the core in the case all of your PEs have TE tunnels between each other. The TE signaled LSP is used in such a scenario to forward traffic from one PE to another.
This has some scaling limitations has the number of PEs grows. In some cases, people use an MPLS TE full mesh between the P routers and run LDP on top of the TE tunnels so that PE routers will use LDP to signal LSPs between each others.
So in short, you can use MPLS TE, LDP or a mix of both to create LSPs between the PEs in your network.