I was wondering if there are any performance benefits for one over the other? It seems like both will work just as well for one-off animations, so the question is whether is such a situation, someone should create a bunch of animation montages to have them precompiled, or generate them dynamically on the fly.
I would assume anything that is pre-made would be more efficient than something that needs to be generated on the fly. Even though UE4 is very efficient when it comes to animations, dynamic generation always has some overhead that goes with it.
What you can do is try by yourself with one way first, then with the other, while profiling each time using the CPU and the GPU profiling tools. Then compare the results. This will tell you for sure whether one is more efficient than the other and if there is a lot to be gained in opting for pre-made vs. dynamically generated.
If you do find out, please share your results so others can refer back to them.