Good question,
The stockpot is a vessel you use to collect traces of metals in solution that may not precipitate from your solutions, or you may miss normally.
Say I have some gold with tiny amounts of platinum, I have processed, and I had precipitated my gold from this aqua regia solution, there was only traces of platinum, so it made no sense to me to concentrate the solution and try to precipitate the platinum, which may have been senseless to try anyway, if I did not have much in solution.
My solution after this process of precipitating the gold would go to the stock pot, as well as other solutions containing traces of values, and sometimes bits of metals that may have trace's of gold or other values that may not dissolve completely, or small bits of base metals with traces of values, my solutions fine gold, as well as other values in solution I have added that I may have missed in solutions, can cement out on base metals in this pot, the base metals here can also go into solution, assisting me in getting values from them, and removing the base metal from these as well, this stock pot collects what I would miss and have disposed of as waste if I did not use the stock pot to collect these.
I cannot explain it as well as Hokes book does, if you wish to know how to use and collect the values from the use of keeping a stockpot I suggest reading Hokes book, a download is found in the book section (or a link under many members posts palladiums posts have the link)
Read Hoke's and learn how to keep a healthy stock pot, and how to recover values from it this pot could be considered a rainy days savings fund, or pot of gold not lost.
The stock pot is a savings account, money not tossed out with the trash.