UA (short for "User Authority") is an alternative "influence metric", like your "57" (right now) reputation score. Where this "reputation score" is computed simply by how much rewards you've acquired over time, UA doesn't look at your rewards / earnings per se, but at who is following who. A (very complex) computation system, lots of number crunching, was invented (by me), then coded (by @holger80 in direct and intensive cooperation with me), to compute (and frequently re-computed) every account's UA score and rank.
@steem-ua is one application that utilizes UA data: you can delegate to it, but unlike a "promo bid bot" it then doesn't upvote your posts by how much you've delegated to @steem-ua but by your UA scores compared to others. It uses 3 components: your own account's UA score, all UA scores from the accounts upvoting your posts, and the same for all accounts commenting on / engaging with, your posts.
Then this way, Using UA services will be beneficial only in cases, if a whale upvotes my post or comments on it since my UA score is obviously low and I would need some whale engagement to effectively get benefit from steem-ua services.
Is it so or should I give it a shot by delegating?