1.7 or 1.7.1

Hello,

Can anyone kindly tell me whats the exact difference between 1.7 and 1.7.1?

I would like to upgrade, but only if necessary... it was not a great luck for me to go from 1.6 to 1.7, not at all.

Please also feel free to suggest, why it is important over the last one?

Thanks for your motivated answer...in advance...