At times, I will see other commuters out there that have a tiny little red blinkies on the rear of their bike, and nothing else.
I don't get it.
Cars turning on to the road from side streets, and oncoming cars making left-hand turns may not see - or be looking for an unlit shadow on the side of the road.
Also, I use my lights not only to be seen, but to see. It's hard to see potholes and other debris at gets pushed into the bike lanes and the sides of the road without lights - heck, it's hard to see them even with! A few weeks ago, I slashed my tire on some broken glass in my lane, because I didn't see it.
If you're dedicated or committed enough to be out there riding every day, invest in your safety. Buy some lights for the front of your bike.