I understand now. This really comes down to LDP vs RSVP as a signaling method.
The benefits of LDP are really simplicity. It is a very plug and play protocol. You turn it on and it just works. For better failure detection and recovery, LDP relies on the IGP to provide those capabilities. Like you mention, loop-free alternates, is a excellent additon to protect MPLS traffic when using LDP.
LDP is still very limited in it's TE capabilites (it relies on the IGP to do the work). I wouldn't even call it traffic engineering. RSVP, on the other hand, has many more options and capabilites. LDP will never match RSVP capabilties.
If you want simple LSP (really a FEC) setup with basic failure detection and recovery, then LDP will be the best option. For everything else, you need to use RSVP. Larger networks combine the to singalling methods by using LDP at the edge of the network with RSVP in the core. LDP tunnelling over RSVP LSP is also used.
I am getting ready to to take the JMV course and it seems like your questions may be covered by this course. So you might want to give it a shot. Here are the course objective. I have heard from a few people who have taken that course that it is quite comprehensive.