What does having Mauer back mean?

Over the course of the season, obviously, having Joe Mauer back will be better than not having him back. Through April, however, it was as though the Twins still had Mauer batting for the catcher every day. Jose Morales spent April hitting in the mid .300s, lining 3 doubles and hitting pitchers of either handedness effectively. The only statistic he was lacking in was RBI, and that had more to do with the futility of players batting in front of him than Morales' own problems.
No doubt Mauer's ability to call games will help the pitching staff. After a few rough outings from a young staff, it is apparent that the Twins needed a guiding hand behind the plate. It doesn't hurt that his arm is much better than Morales' as well.
The thing that many people were waiting for from Mauer, however, was his offense. As I already mentioned, Jose Morales did a good job at the plate, hitting .349. His offense was squandered, as he was often hitting ahead of Nick Punto, Denard Span and Alexi Casilla. Span is no slouch, but thats practically 2 two guaranteed outs behind him in the next three batters. Mauer, because Gardenhire trusts him more, will be batting third with more support behind him. Essentially, Mauer's presence will cluster the best hitters better than when Morales was in the lineup for no other reason than Ron Gardenhire is more comfortable with Joe Mauer.
Of course, this ends up creating strange situations like the one seen in todays game. Delmon Young, who has the highest average among regular right handed hitters, is batting 8th. When Morales was in the lineup, Young was often placed in the 7 hole. Nevertheless, having more good hitters batting in a row is a better idea than having them scattered. Now all there is left to do is to move Casilla out of the 2 spot, and move everyone else up one, or to give Brendan Harris a little more paying time.
Basically, what it comes down to is that the Twins are a better team with Mauer in the lineup not because he IS so much better than the alternatives, but because the Twins expect him to be.