What do voidstones actually do

So, I now have all 4 voidstones, making all my maps t16 on the atlas.

I am so confused about their actual effects though. The maps level didnt go up, they dont count for maven etc. So can someone explain to me what socketing 4 voidstones actually does?

It doesn't level the maps you already have to 16.

It just means all maps can drop as level 16 now.

They also each give 25% chance for maps to drop 1 tier higher.

You can also put sextants on them to further juice up maps