If so, I guess trimming 357mag brass should be more important.
Kinda....
because crimp is more important in the .357Mag.
The .38 Special sits right on the border between needing a crimp, and not. Standard velocity 158gr .38 Special (850fps approx.), fired from a "full size" (aka heavy, such as a S&W N frame) revolver, and assuming
proper neck tension of the case on the bullet, don't need a crimp.
Same exact ammo, fired from a lighter gun usually needs some crimp to prevent bullets moving forward. A light crimp usually works fine.
The same load, with a light crimp, fired from the lightest guns might need more crimp to prevent crimp jump.
The same pattern applies to all what differs is the amount.
The heavier the load, the more recoil, the more the revolver cylinder acts like an inertia bullet puller. The lighter the gun, the more recoil, same effect.
So, at .357Mag recoil levels some crimp will be needed, even in the heaviest revolvers, and very light revolvers (like snub noses) may need a very heavy crimp.
Trimming is the preferred method of maintaining case length uniformity. Uniformity means you aren't needing to adjust your dies for each individual round, and one setting doesn't over or under crimp.
MEASURING is the first, and vital step. Take a look at the bullets you are going to use, note the size of the crimp groove or cannelure. Some are fairly narrow (most jacketed bullets) some cast slugs are much wider.
Measure your brass, find the difference between the longest and the shortest. IF that difference is small enough that the shortest case will still be crimped into the groove if you adjust your die using the longest case, it will work and you won't need to worry about trimming. (at that time).
And when I say it will work, I mean the case will be crimped in the right PLACE on the bullet, not that it will be the right amount of crimp for your specific combination of gun & load.
Crimping outside the groove, or when there's no groove is easily overdone, and that is a bad thing, it may distort the bullet, or buckle the case, even to the point of preventing chambering.
You CAN crimp lead bullets outside the groove, lead is soft, but there is a limit, you can go to far. Trial and error is the only way to get the "right" amount for your needs.
Trimming all your brass to the same length as your shortest cases means there's no worry about over or under length cases resulting in too much, or too little crimp, and once you adjust your die correctly for that length, and desired amount of crimp, you're set for all your brass.
Total case length in revolver rounds isn't as important as it is in other kinds of guns & ammo. As long as your brass isn't so long it hits the ledge at the front edge of the chamber, (and that is a significant amount above listed case length max dimensions) it will work fine.
In other words shorter than max or even shorter than "trim to" length cases work fine in revolvers. As long as the length of the brass is uniform for ease of reloading, its all good.
One note about batches of brass, it has been my experience that with pistol cases, some stretch different amounts and some even get shorter. If you check your brass and find that out of all of them you've got 2 or 3 significantly shorter than the rest, then its decision time. You can either trim everything down to the very shortest ones you have, and load them all uniformly, OR you can trim to the length of the shortest of the majority of your brass, and the very few shorter than that can either be tossed, or loaded as individuals, adjusting for their length.
Despite it being more than 45 years ago, for me, I can still remember the time when every case, every primer, every bullet was a precious and valuable thing, and a ruined case or primer was almost enough to justify tears. (ok, I was always that cheap
), Today, I'm well past that point (though still pretty cheap by most standards) but I can still remember it...
Up to you what, and how you do it. What works for me, may not be worth it to you.