Yes, that link seems to be broken or internal (even NetApp partners cannot access it)
To answer your questions, there is only one reason where Aggregate snapshots can help you, and that is if you need to restore a COMPLETE aggregate (with ALL volumes in it) to a previous version, for example if you deleted a volume by accident. There is no way to restore single volumes from an aggregate snapshot. It might also help with recovery if you should ever get a corrupt WAFL (highly unlikely).
The default for NetApp systems has been for quite some time now to disable aggregate snapshots completely. The only reason you might still need them is if you're running MetroCluster (or Local SyncMirror) because then the Snapshots are needed for mirror reconstruction. But that's something that happens behind the scenes and doesn't help you as an admin with anything
So yes, feel free to disable Aggregate snapshot reserve (if you're not on a MetroCluster)