That Maya speed is not only for super complex rigs for movies - it allows to animate at double (or more) FPS, getting a much smoother movement, it allows to have a multiple transformation structures always available for animating, so on.
Most studios have custom solutions as parallel rig evalution isn't robust.
Here Maya Parallel works really nice and predictable, much smoother in Maya 2017 than in 2016. Perhaps a part of that ‘predictable’ belongs to around ten years of my playing with lazy evaluation system in Softimage. Yeah, some experience is needed to recognize is it just a ‘too lazy’ evaluation sometimes, or there's some error on road. Such system is always sensitive to hierarchy structure.
Really don't know what happened with these studios, which practices they had before and how that fits to current Mayas, is there something else that counts. Not enough info for anything useful for me (as usually).
Let's say from Softimage perspective, reliability of Maya Parallel against SI (classic) kinematics is comparable to ICE - Houdini SOP-VOPs ratio. Some parts are different but generally, after some time it's possible to be focused on creation, having a ‘rules’ stored somewhere in ‘intuitive part of brain’.