When I was learning BSL (British Sign Language), I wanted to be able to note down words I had learned, or the ability to look them up. It was part of how I studied. At the time, all that was available was https://en.wikipedia.org/wiki/Stokoe_notation which is a complete pain to try to use. Sutton SignWriting looks to be similar in that sense. As others have said, much like IPA for language learning.

Of course video is more easily available now, so there are some aspects of study that may not need the ability to write things down.