Saved vs Unsaved Raid

I’ve never understood exactly what the difference between a Saved vs Unsaved Raid is… anyone? It’s so confusing. lol. Also does it even matter on non-mythic raids?

It could be the lockout. You can only fight a boss once a week. And if other people join your raid the bosses won’t be there for them, assuming it’s your lockout.

Means slightly different things on mythic and non-mythic.
On non-mythic, when you kill a boss, you are saved to that boss, and can’t get loot from it again until weekly reset

On mythic (and most raids pre-siege of orgrimmar), saved means you are saved to that specific raid ID. You can’t zone into a different instance ID at all.