I've been trimming all of my brass since I began reloading years ago. I know that generally speaking, it is not considered particularly common for most reloaders to trim pistol brass, but I learned from a book and followed the process to the " T ". I don't notice any particular advantage with rimless cartridges such as 9mm, .40 and such. But with revolver, or rimmed brass, I do appreciate the consistent and solid roll crimps it facilitates.
As for bottle neck brass, I consider it an absolute necessity. I keep those trimmed to exactly the same lengths and some where in between trim too, and maximum.
GS