While some dreams can appear to be more self-explanatory than others, even those are often filled with symbols and multiple layers of meaning -- but exactly what that meaning is depends on the dreamers.
Although it is tempting to think of "daily residue" dreams as unimportant, the process of decompressing from daily events or getting clear about what needs to be done the next day are very important -- even if they are experienced as less exciting than some other types of dreams.
There is not one answer. But everyone does it. It's as natural as breathing, and just as much of an involuntary activity -- even people who don't remember dreaming actually do, for at least one to two hours every night.