United Club access on an I-D connection when the arriving international flight is on a *A partner.
Otherwise, as OP is likely already aware, there are few if any *A benefits when flying premium cabin.
The benefits come into play when flying Y (for example, on an intra-Europe award). That's when the business class check-in, free baggage allowance, gold track security, lounge access, early boarding, and (in some instances) preferred seating all make me very grateful to have lifetime UA Gold.
If the passenger is based in LAX, as Gold, they can visit the Star Alliance Lounge, whereas they would not be able to access with domestic F tickets or the United club membership.
UC membership will get you into the *A lounge on a domestic itinerary.