Mozzarella, tofu come with a liquid, I think is whey. Is it useful in any way? has this any culinary value?
The purpose of this liquid is to prevent the cheese or tofu from drying out. Its main use is for storage, not for consumption. If you don't consume the cheese at once after opening the original package, you are supposed to transfer the liquid into a storage container, or replace/fill up with water.
There are people who drink the whey, because they like the taste. There isn't much to be said here; they pour it into a glass and drink, without further preparation.
Otherwise, any recipe which uses water can use whey instead. The taste difference for mild wheys such as mozzarella and tofu whey will be very slight, almost unnoticeable. There is nothing special to take into account, except a small probability that you won't like the taste and would prefer to use water instead. There is no way to predict whether you will find the taste harmonious: it is a personal preference.
A known use for the whey created during cheese making is to make ricotta. It will not work with tofu whey, and I don't think it will work with the liquid in commercial mozzarella packaging either; you'd have to make your own cheese to get the necessary type of whey for ricotta.