What is the advantage adding the inductor in balun circuit?

Hi friends,
The attached is for 900MHz receiver balun circuit. I know balun need to 180 degree phase difference between two balance output ports. And anyone can tell me why add L3? Has it advantage?
Thanks,
[url=http://images.elektroda.net/47_1237196202.jpg][img]

Added after 7 minutes:

The inductor in front of the differential LNA will improve the common mode rejection and also to reduce the second-order distortions.

Thanks,vfone,can you expain them or share me some documents about two cases in detail ?And how to select the inductor value?
Thanks

A few Ω will increase (improve) common mode - inductor have a few Ω.

When your worked with diff mode by default you IM2 very good

Thanks,DDavid.Any documents introduce differential mode reducing IM2？