In a recent thread about the Malte Power Reserve with Date model (click link below) a question rose as why ceratain
Vacheron Cosntantin watches had saphire crystal backs and other had closed case backs.
The reason of course has nothing to do with the quality of movement finish which is the same regardless as to whether the movement can be seen or not (I think that it is important to stress the point that the finish of the non visible and underdial components is done at the same level as the visible parts putting Vacheron Cosntantin on a level few brands can comete with...but that's for a seperate articel :-) )
The reasons are mostly aesthetic or functionnal:
1) The movement is considered small compared to the case size (ex patrimony Contemporaine manual or in a lesser event the Malte Power Reserve/Date). This does not mean however that VC will stop using smaller movements in bigger cases because it is the case's aesthetics which will dictate the type of movement to use and for example to obtain a slim case (like in the Patrimony Contemporaine manual wind) only a slim movement can be used and a slim movement can only be small in diameter
2) The case form and the movement form differ (round mouvement in tonneau case)
3) Technical necessity: for example the soft iron inner case of the Overseas
Hope this helps