I think all armed citizens should carry OC spray as part of their daily carry. As I have written before, even if you are a tough guy that is good with your hands, you should carry spray because it is actually a lesser level of force than putting your hands on someone. If facing a deadly threat that is imminent, a deadly force response is in order, not spray. However, if facing an impending simple assault that you would be justified reacting to with your hands, spray is usually appropriate and may be a better option in certain circumstances. Spray allows you to potentially avoid making contact with the aggressor, and it can often take the wind out of the sails of an assailant so that you can break contact and get away. Of course, a determined threat will not stop with spray and may escalate the violence to a higher level, but that is what your handgun is for.
In our modern world of political protest and mob violence, pepper spray is ever more important. Aggressive action, such as slapping hats off heads, blocking people from exiting a restaurant, or spitting on those with differing political views, does not justify a lethal response, but typically does justify spray. A face full of spicy goodness does wonders to break up a mob of miscreants. Since most such individuals lack the courage to carry out such social justice on their own, they usually rely on numbers. Superior numbers makes such hostility more threatening and potentially more dangerous. Spray can often tone down the zeal of aggressive social justice warriors and cut short their escalation of violence, providing you the opportunity to leave the situation and escape safely without needing to escalate to higher levels of force.
Some consider spray a substitute for heated language or a way of winning an argument. If you spray someone because they insult you, be prepared to be arrested, and rightly so. If you spray someone because they cut in front of you in line or spill your drink, be prepared to get arrested and prosecuted for assault. Some people feel that spray is somehow an unrestricted tool to be used for any sort of retaliation against a social transgression. It is not. Generally, spray is justified if using force with your hands is justified. Is putting your hands aggressively on someone, or striking someone, justified in a particular scenario? Under those circumstances the spray usually will be. Short of that, perhaps not. Spray can be used preemptively, but you need to be able to articulate that you had a legitimate fear of assault. When being aggressively surrounded by a mob, that justification will be evident if the crowd gets hostile.
A further consideration is the spray that you carry. I admit that such modern mob activity has me re-evaluating my own carry. Typically, I use a key chain size unit that has a cone delivery pattern. These are easy to carry, but limited in capacity and range. Also, the cone type sprays are easier to hit the target with, but it is very easy to become contaminated with the spray yourself. If you need to deploy spray while around your family members, giving your spouse or children a dose of spray is not ideal. A stream delivery is much less likely to contaminate bystanders. A larger duty size unit that has a stream pattern may be worth carrying, despite the inconvenience, in our modern age of mob rule.