I've carried a surefire of one kind or another ever since they came out - both in corrections / law enforcement and in personal civilian life too. I know from use that the bright light can help distract and can provide a few second's edge in your response to a situation.
There is another fact too... in a defensive situation where the aggressor has been distracted by the bright light - you have a very hard impact tool in your hand that can then be used to add a strike (if or as needed) to add additional response to an aggressor's actions. It's all a continuum in the use of force... sometimes the light can be enough to defuse or deflect an undesired response but I'm always glad to know I have the option of a follow up with an increase in response level and an 'alternate' use of my flashlight.
I also many years ago had a firearms instructor who I and many of my professional colleagues had very great respect for flatly state it's far better if you have to pick only one to have a flashlight with your sidearm rather than an extra reload - ideally both but the flashlight wins out when you have to pick.
Paul in MN -