Becoming an authorized user on someone else’s credit card can add that account’s history to your own credit report, which sometimes provides a meaningful boost, especially for people with a thin or new credit file.
The benefit depends heavily on the primary cardholder’s habits. If the account has a long history of on-time payments and low utilization, it can help. If the account has missed payments or high balances, it can hurt the authorized user’s score just as easily.
Not all card issuers report authorized user activity to credit bureaus, so it is worth confirming beforehand. This arrangement works best between people who trust each other’s financial habits completely. This is general education, not a recommendation.