The instances where I find the headlight most frequently useful to avoid two fists of brake levers are 25 MPH roads, w/ stop sign cross streets where vehicles don't wait for right-of-way bicycles. My less frequent usage on 45 MPH unlimited access commercial area roadways is also useful for the extra visibility.
When I'm riding on roads w/ lots of bikes my opinion is that my
Cygolight Hotshot Pro 150 red rear taillight is much more valuable, especially because I'm sharing the roadway, w/o a dedicated bike lane, except for infrequent places.