I always do online check-in first at home after the following experience:
We were flying out of DTW to Japan. DTW is a 2 hour drive from our home. I rarely did online check-in at that point, but I did this time on a whim.
When we got to DTW there had been a huge system failure and they could not issue boarding passes. Since we had ours, we got on. The flight, almost always fully packed, was half-empty, with many folks sitting sadly at the airport. If I hadn't printed them, we would have had to wait until the next day (if we were lucky) to get out.
As someone else mentioned, you can always print new BPs at the airport if you want
I'm now religious about printing my BP at home, even if I have checked bags.