Watching the following video of HandMade Hero, episode 20:

https://youtu.be/hELF8KRqSIs?t=1h25m23s

I can't really understand the purpose of SoundOutput.SafetyBytes.

Isn't the WriteCursor already offset by the amount of time since GetGlobalBuffer->GetCurrentPosition was called?
If so, what does SoundOutput.SafetyBytes measure?