They can dividend it, use it as capital, or use it to increase working capital (like stock.) Some tax environments tax dividends further, thus making it attractive (or cheaper, depending on you pov) to reinvest the profit in the business.

Of course working capital (stock on hand) can also be increased by other means - for example a loan or a capital injection.

Lastly, raw stock (pile of chips) is easy to value for stock-taking purposes (usually cost basis.) partially, or in some cases completely, finished goods is trickier. They could be valued at cost, at zero (a half finished controller is worth, what?)

Generally companies keep as much as they need, ideally no more. But the right number can be a moving target. We've been erring on the high side for a while now.