simple question about calculated bc
 

Hi there foamers - I have a simple question. I have seen that some tutorials specify a value for boundary conditions of type: calculated. For example a velocity field bc patch input might look like:
patch1
{
type calculated;
value uniform ( 0 0 1325);
}

Is it necessary to specify a value for this type of boundary condition? Does specifying a value change the simulation?

Also, it seems that for different boundary condition specifications I get different output fields. I have been using dsmcFOAM and have noticed that cases output different fields, and my only guess why is different bc specification.

Thanks for all the help.