PP - the FMC is really an 'advisory' system and works out its descent in its own way, with the LNAV constraints you mention. It is often not close to my mentally derived predicted descent path, but in deference I have always assumed it knows more than me - whether I let it carry on....................? It has often led me into uneconomic descents and sometimes (always on the VOR R35 PRN) abandoned me and left me to sort out its mistake.
In answer to to your 'implied' question, it is your choice whether you react to it - or even use it.
It is not worth trying to outthink it. Best to 'monitor' it and be 'aware' of its advisories.