So, I've been seeing some people talking about using the same yeast cake for multiple batches during fermentation. What exactly is this? My thinking is that when you brew two batches that use the same type yeast, after your boil for the second batch, you pour it in your primary fermenter overtop of the sediment in the bottom of the fermenter that is left over from the first batch. Is this correct? If so, what is the advantage of doing this? Saving the $4 or so another thing of yeast would cost?