At the very, very least he is a warm body. After losing both Jerricho Cotchery and Emmanuel Sanders via Free Agency the depth behind Antonio Brown was scarce to say the least, so Moore will at minimum bolster what was becoming a rapidly depleted receiving corps.
But simply being a live, functioning human is not the end of what Moore adds to the Steelers. At 31 years old, and after 7 years with the New Orleans Saints Moore is an experienced, veteran receiver. He has been in the league since 2005, and he's seen and done it all. That includes playing in and winning the Super Bowl in 2009.
His experience playing in a prolific offense with a Hall of Fame level quarterback should be of great use to the Steelers, not only on game days but in helping develop second year receivers Justin Brown and Marcus Wheaton, as well as third year receiver Derek Moye. A proven veteran in the film room and on the practice field can do a lot for the development of young players in terms of teaching and leadership. Prior to signing Moore, Antonio Brown was the oldest receiver on the roster at age 25, and adding an older head like Moore should be a positive for a young Steelers receiving corps.
Moore also brings proven production with him from New Orleans, something that is sorely lacking on the depth chart. For his career he has 4,281 receiving yards and 38 TD's, both of which trump by a mile anyone on the Steelers team not named Antonio Brown. Derek Moye and Marcus Wheaton combined boast 8 career receptions and 84 yards, so adding a proven contributor like Moore ensures that the Steelers have a receiver outside of Brown who has shown he can get the job done. In fact, Moore put up 1,041 yards and 6 TD's in 2012, which is impressive numbers for any player.
And finally, I'm saying this with fingers crossed, Moore may prove to be a bargain for the Steelers. The Steelers did not match Cotchery's two year $5 million deal with the Panthers, so obviously Moore is signing for less than that. Even though he has been productive for the Saints in the past, injuries severely limited his output in 2013, and he found himself looking up at rookie receiver Kenny Stills on the depth chart. This will have pushed Moore's asking price down considerably.
Coming off an injury marred season is obviously bad for Moore when he is searching for a contract, but it may prove very fortunate for the Steelers. If Moore can return to a level close to his 2012 performance, the Steelers will be getting a serious bargain. It's a very low risk signing, with a potentially quite high reward in return.
Some fans may bemoan Moore's short stature, and at 5ft 9 inches he is certainly short. But the Steelers are not planning on Moore being that "tall" receiver Roethlisberger has been pining for since Plaxico Burress, they are hoping he can replicate or improve upon Jerricho Cotchery's production as a slot receiver. If he can in fact achieve this, then he will be have been a good signing for the Steelers.