It is a very basic question that up to now I don't quite understand. あげる just gives additional information about the direction of action. Because 貸す provides direction of action clearly, I think あげる is no longer needed.

In other words, sentence B below should be more efficient than the sentence A without loss of any meaning. What do you think? 

> 
> A: 僕は君にお金を貸してあげた。
> 
> 
> B: 僕は君にお金を貸した。
> 
> 
> 

In English they are both translated to "I lent money to you.".