Fallout 76 allows teammates to share Perk Cards between them. The basic rule is that you need 3 current charisma per 1* of card you want to share. Current charisma, not SPECIAL charisma - SPECIAL stats are only considered a foundation for your current stats, and when defining how many perk cards you can use. When in-game results are calculated, they are calculated from current stats, which are influenced by armors, aid etc.
So if you play lowHP build, and have 3 charisma and lets say 9 bonus from unyielding set, if your current charisma is at 12, and you can share 4* perk cards.
This provides excellent results in well-coordinated teams. Know the feeling when you can't choose between one card and the other? Pick one, let your mate pick the other, share them between you so you both have two.
There's a card - magnetic personality. It gives 2 charisma per each team member (excluding you), which means in 4-people team it gives you 6 charisma. If you share it to your team, each teammate gets bonus 6 charisma.
Rarely anyone has charisma lower than 3, and the extreme PvP builds with 1 charisma most probably run with Herd Mentality that puts their base charisma at 3 or 4 (with strange in numbers). This basically means that if 2* Magnetic Personality is shared in 4 people team, practically everybody in this team is now able to share 3* cards back, netting you an easy 9* bonus to your active special.
It's important to consider the nature of the bonus charisma effects. For example, if you use unyielding armor and heal your rads so that your armor reduces the bonus given, you'll stop sharing. If you play in four person team with Magnetic Personality shared, and one team member gets disconnected, whole sharing will collapse.