For my light plinker loads? Once, never again.How often do you all have to trim 357 mag cases?
For my full power loads? Sooner or later they will need it once more.
I trim all revolver brass in the beginning, unless it was bought all same headstamp. I also chamfer and deburr it, including same stamp bought brass.
I use nothing but range brass for .357 Mag, and the lengths are all over the place because of all the different headstamps. Making them uniform really makes for good consistent crimps and start pressures. Same thing for .38 Spl range brass.