First, preface my response with info...
EDC = Preon 2 Ti, in rear left pocket. And HDS Rotary in dropin EDC bag, usually in briefcase/gym bag/etc bag. Spare sets of cells for each in EDC bag as well.
Okay, now here's my truth.
99% of the time I would be fine without an EDC. There are very rare occasions when I have neither EDC light in my possession, however those are rare occasions. I work in finance so my job is a regular office job. No long dark stairways/hallways either, so during the day there's literally no reason to have a light for emergency. There are however, utility reasons. Setting up projectors, TVs, computers in rooms that are poorly lit. Fixing the printer. Other boring stuff.
But the real reason I carry a light is for the "what if..." scenarios.
What if I choose to head to the bar after work for a mates birthday? Yup, can't drive home, close enough that I don't want to pay for a taxi but the streets are poorly lit. Got it covered. And yes, it has happened.
What if a circumstance arises that prevents me from getting to my car/to home until late?
And the last reason, 0.00001% probability ... What if the poop hits the fan while I'm at work? Clogged roads means home is 2 hours away on foot. I'd rather have a limited supply of essentials, which includes light, instead of nothing. Especially when the price is only a few ounces a day.
To the guy who hates stuff in his pockets ... So do I. I barely notice a light in my rear left pocket though, and forget its there usually. The bigger light and spare batteries go in the EDC bag which usually contains what I need for regular stuff (gym clothes, work files, beach towel, etc.).