When you want to leave someone a quick message, you often write it down on a sticky note and paste it to the relevant location. Alternatively, you call to leave a voicemail. Holo Voice Memo lets you do both at the same time by leaving an audio clip on a physical object in the room so anyone with a HoloLens and the app can play it back.
While the video above demonstrates functionality more than utility, you can see how easily one can leave information for others. In a similar manner, this could be used for tours around homes for sale to leave contextual information, or in museums to help educate about specific exhibits. In your own home, you could leave messages for your housemates to warn them not to eat the cake on the counter or that the dishes in the dishwasher are clean.
Wearing a mildly bulky headset just for voice memos may not make a lot of practical sense at the moment, especially when few can obtain and/or afford one like the HoloLens. As the technology progresses, however, it's this kind of software that we'll likely use on a regular basis to leave and retrieve relevant information in our collective mixed reality.