I understand the need to use the 3D Reflector updating script to update the composition to ensure all the reflections are properly updated in a comp when previewing, but what I'm not sure of is, do I need to update the comp just before I render out the final footage, or is the script to be used just for RAM previewing etc?
You shouldn't need to update the Comp just before rendering,
but it's probably not a bad idea.
We have the Update button/script because we use some aspects
of After Effects layers that don't get passed on to us when they change.
For example, if you have applied Reflector to a 3D Solid, and then
move or rotate that Solid, we aren't told by AE, so we don't know to
update our reflected Comp.
Therefore, as a practice, if you can put it in your workflow, it's a good
idea to Update before rendering. In many cases, you won't need to,
but there's nothing worse than waiting an hour (or seven) just to see
that the reflections are off.