Dice introduces "Premium Friends" - a feature which lets the Battlefield 1 players access all maps in the game without a Premium Pass. As long as there is one player with a Premium Pass in the entire party, the party can access any map available in the game. However, only the Premium Pass owners get to enjoy certain benefits.
Dice are introducing a plan which will, they hope, alleviate "the potential friction when playing with friends where some own a Battlefield 1 Premium Pass and some don't." They may have found a solution which will make you the belle of the ball if you're a proud owner of a Battlefield 1 Premium Pass, and they're calling it Premium Friends.
The Premium Friends approach works like this: if you form a party with a player who owns a Premium Pass, your entire party becomes "Premium Enabled". That means you can access all maps regardless of whether you own the content they are a part of or not. "The access is available as long as the party is Premium Enabled."
There is a catch of sorts: while all players belonging to a "Premium Enabled" party can access the maps, only the players who actually own the Premium Pass can reap the benefits.
Those benefits include earning the experience from the map or the specific expansion pack the player owns, only the owners can spawn in with weapons and vehicles unique to the map or the expansion, and only the owners can "track progress towards the unique medals and codexes for the expansion".
Good news for everyone else - the XP you earn in the map you don't own will be saved and retroactively given to you as soon as you purchase a Premium Pass or the specific expansion.