If you use these, gone are the days of A4 sheets of music fluttering off the music stand when a draught or gale force wind catches you unawares. Also sheet music that doesn't want to stay open on the page you need whilst you are playing can be pinned down with these little marvels.
Don't expect these small but powerful magnets to to be strong enough to hold thick music folders or music with hundreds of pages (but they might be able to with some improvisation on your part). For most music and performances these magnets are really great. They are more discreet that the clothes pegs or bulldog clips I used to use, and less fiddly than blue tack. Obvs they only work on music stands made of metal!