Why is there a lame duck session?

I find it odd that people who have been voted out get one more chance to pass laws without consequences. Is there a reason for this? I get the need for some delay time between elections and getting sworn in:moving logistics, in progress negotiations, bringing the new guy up to speed. But really I think it would be better to move to be closer to the swear in date and not have the lame duck session.

tl;dr Is there a reason for having the lame duck session?