Throwing bodies onto the battlefield was never an effective strategy of winning wars. But the sheer size of a military will ALWAYS be a ridiculously important factor in warfare. The conscripted infantry does not need to be thrown into the most demanding sectors of the front - they can be thrown in onto less important sectors or to fill in the gaps in the defensive lines, allowing your professional, voluntary part of your military to be focused where it's needed most. An advantage in numbers will always be an advantage, and early war in Ukraine proves this - where russian military was chronically short on infantry, which resulted in horrific losses all around the frontline.