Imagine you have to communicate something precise to me and I am stuck in a meeting:
- you send me a picture, it may be ambiguous;
- you leave me a voice call, I have to go out of the meeting room to listen to it
- you write a message, it just works. If there is info to use, I will easily copy your message in any application (Excel, Word, SAP...).
Also, text can be stored easily, so I will keep an archive of your text, probably far less an archive of your voice message or diagram, as they are very heavy.