Let's say you have a witch, for example, and you've used conversion spell to make a bunch of metals, but you haven't collected them them yet. Say you're saving them for another sim to collect. But metals in particular, and some gems look very similar. You want to distinguish between them all. So you place a floor label - and put the corresponding metal in that space/row. The only way to tell what a metal/gem is before it is collected is to pick it up in buy mode.
Or, say you have some stacks of metals that you want to be able to see what they are at a glance, rather than having to hover your mouse over them. You could use it that way, too.