Not all crenellations are aggressive looking strike bezels that will tear and snag things they come into contact with (whether wallboard, pockets, or "softer" materials.) Strictly as a matter of form not function this bezel is more pleasing to my eye than if it was smooth.
Of course you mostly seemed to want to talk about the more aggressive of their brothers. By reducing the surface area being contacted initially more force will be delivered per unit of area being impacted (with the same total force being applied). That's going to make it more likely that the material being impacted is going to be overwhelmed at the point of impact. You can probably expect that in many cases you'll see more penetration on the impacted target.
That's very similar to what the thinking is in the design of Armor Piercing rounds used to defeat main battle tanks. Terminal effects are only part of the equation though. To defeat a tank you have to both hit it and produce a desirable result from that hit.
A strike bezel increases the odds of a beneficial self defense result given a hit. It's on an improvised weapon that may or may not offer a reasonable chance of successful hits (depending on training and other individual factors.) If the odds of hitting with it are low the effect of a hit may not matter. Carrying it involves costs - increased size, weight, clothing wear, etc.
Both the chance of it being applied correctly, and the costs, are issues that are very much dependent on personal factors and weightings. Other options for self defense will also be heavily weighted by personal factors, and wildly differing laws.
Blue you ask if I think they are a positive addition to a light. The more important question is are they a positive addition to a light carried by which person, in what circumstances. I don't think we will ever come to a consensus. The only consensus that truly matters is the consensus of one - the one carrying the light. I don't choose to myself. I won't say that I can't envision times when they make sense.
