I disabled my DRLs because I like the choice to have my
headlights off if I want them to be off (eg. sitting in a parking lot or waiting for a friend in their driveway). I also would rather "off-on" flash semis than "high-low" as a courtesy since I used to drive over the road and I liked that better.
I use my
headlights when it gets dark. I use my fog lights when it is foggy. I turn on my parking lamps/driving lights if there is low visibility.
I do not believe it is illegal to disable the DRL on a vehicle that comes equipped with it, but I'm sure my insurance company would frown upon it since it is listed as a safety feature on my car. Yes, I do believe it is safer to drive with lights on at all times as I did it when I drove professionally. Do I think it is necessary? No.