We would get soooo much insight into how life begins, commonalities, would these bacteria have rna or something similar, etc.. So damn cool, too bad the theory is a deep drilling operation to get to the possible life.
Certainly makes me really optimistic that life could be found in the frozen moon of I think it was Triton which has an ocean and possibly the basics needed for life.
If nothing, confirmation on Mars and finding something different say on Triton would radically change our understanding of life, and change the idea that you need very specific conditions for life to begin.
Edit, it was Europa which I was thinking of:
http://www.solarviews.com/germ/europa.htm