It means to pointlessly take something to a place that already has it in abundance.

As someone who’s spent a lot of time working in a lab, the ability to control static electricity would be a godsend! There’s really nothing like spending weeks preparing a new material as a fine powder, carrying it over to the weighing scales, placing a glass sample vial onto the scales, taring it, then a scooping up some of your powder with a spatula, careful not to lose a single particle, then carefully, CAREFULLY carrying the scoop of power to the sample vial – then seeing the static blast your powder out of the spatula to coat the OUTSIDE of the sample vial, plus the scales, plus your nitrile glove…

I have trauma.