[Helium]

Hi guys,
I need an explanation about UDF. Take a look at this topic:
CG Motion UDF Problem

I use something very similar to this:
I define a sinusoidal function for the velocity along x-axis, I compile the udf and decide what part of my mesh I want to move. It works perfectly: the wall moves back and forth along x-axis.

However in fluent manual, just like in this other thread:
dynamic mesh using define grid motion udf

there is a part of the code where the node are updated. The fact is that I never do that and I do not have any kind of problem... but I do not know why.
So is this part of the code really necessary? Yes, no, else...?
I do not understand what this is used for. I do not do it and I have a perfect dynamic mesh layering.

Regards