As a Roblox developer, it is currently impossible to use a sound’s parent as its SoundGroup by default.
It seems intuitive that the SoundGroup a Sound object is parented to would be its default SoundGroup. In fact, I thought that’s how it worked, and it took me a few days to realize I had to explicitly set this.
Across the platform, other properties (such as Adornee) will default to the parent object. I think that this should also be the case with the SoundGroup property.
Example:
Click and Hover should automatically use the UISounds group as their SoundGroups if no SoundGroup has been explicitly assigned to them. Currently, I still have to manually or programatically set the SoundGroup property.