Daytime running lights (DRLs) have been mandatory equipment on all vehicles in Canada since model year 1990. That means we're passing the quarter century mark of the introduction of this safety feature. The final version of Statistics Canada's Canadian Vehicle Survey was published in 2010 and at that point, vehicles older than model year 1991 make up less than 5.5% of the total number of light vehicles on our highways. We should not encounter many vehicles that don't have DRLs during our travels.
In my experience, many people like lights and often add extras to their vehicles, either for a specific safety purpose or for decoration. Why would some vehicle owners purposely disable their DRLs even though it is not legal to do so in British Columbia? The best justification that I could find for this is because the use of DRLs slightly increases fuel consumption. Newer vehicles use LEDs or signal light filaments to provide adequate light yet minimize fuel consumption.
I suspect that fuel efficient driving techniques would more than offset the cost of DRLs and contribute to their safety gain.
DRLs also guard against carelessness or inattentiveness, at least for drivers facing the vehicle. It is a popular complaint from DriveSmartBC respondents that drivers will drive without lights at times of poor visibility. Automatic lighting systems are popular in new vehicles, but until you buy one you do have to remember to turn on rear lights when necessary.