The can substantially help if you have low CL and high util% and your wife has large CL and low util%.
For example all your revovling lines have $5K total CL. You have a 50% util ($2500). You wife has a card with %10K CL and 0% util. Adding you as an AU changes your total CL to $15K and drops your util to 16%.
YMMV but generally getting added as an AU helps the most if:
* your current CL are low and TL CL is high.
* your util is high and TL util is low
* your number of cards is small
* your length of history is short and TL has long history.