Isn't a concept we talk about much in macro. Which is a bit weird, when you think about it. And it's always good to examine the way we think about things, and teach those things.
We talk about households' desired flow of saving, and firms' desired flow of investment, and we talk about the actual flow of saving and investment. We also say that firms have a desired stock of capital, and spend some time explaining how to get a desired flow of investment from that desired stock of capital. Why don't we talk about households' desired stock of savings, and compare it to firms' desired stock of capital, and compare both to the actual stocks of capital and other assets?
I don't know the answer to that question.