I mainly use these for securing pages to a music stand - either directly or through a folder. They're strong enough that they will still work well through a certain amount of intermediary material such as pages of a book or a plastic folder.
Of course, they could also be used as a stylish means of holding notes to a metallic notice board or as fridge magnets.
The shape makes them ergonomic while the flat top allows them to be stacked together which is useful for storage.
The layer of softer material avoids hard metal-to-metal contact which could perhaps tear a page over time. As well as reducing contact "click", it makes for a more refined feel.
I find they also work well in combination with other music stand attachment products such as the board extension folders or nylon-string-and-magnet devices available.