I wear it because I am on the board of the local Bicycle Advocacy group.

Other than that, 40 years of experience weighs against the need for it except for times such as running down high speed mountains and it's uncomfortable.

However, when I lived in the desert, I did find that the helmet did tend to keep my head cooler when riding home in the summer because of the styrofoam insulation.

I have had one motorcycle incident where I was very glad I was wearing a full-face helmet when I noticed it shifting on my head as my face was on the pavement and was happy that my face was not getting torn up at that moment.