Do you mean being an authorized user for a CC? It can provided it helped in the following ways: 1) improved util, 2) improved mix, and 3) improved oyur length of history and/or average age of accts. It can hurt if 1) it hurt util, 2) lowered your AAoA and/or has a very recent open date, or 3) has a negative history.
Just make sure you aren't relying on them. I have seen some examples in here of lenders taking issues to those that have a herd of AUs.
