The deal with not needing to trim handgun brass is pressure-dependent. Very broadly speaking (because it differs some with burn curve shape and brass shape), cartridges that peak at much above around 30,000 psi will have their case walls stick to a chamber wall before the head backs up to the breech, which then happens by stretching the brass where the head thickness drops off (at the pressure ring), causing case growth. Below about 30,000 psi, the whole case backs up to the breech along with the head, and this happens before the case walls stick and fully seal against the chamber. As a result, brass stretching to make head contact does not occur. So, if you have, say, 38 Special, you may want to trim once to get the even crimp Buck mentioned, but then you probably won't have to trim it again.
With low pressure rounds you can actually get some shrinking with each load cycle, especially if you have a tapered chamber, from which brass doesn't always size back 100% to length. I did an experiment with .45 Auto in which I put 500 Winchester bulk brass cases through 50 light target level reloads. Many were splitting or lost in the grass by the time I finished. Of those that remained (about half), all had shortened about 0.025", so they were all below SAAMI minimum and I'd had to adjust my taper crimp die to keep using them. Bottom line, they lost an average of half a thousandth in length per load cycle. There is obviously no cause for trimming at that point. Indeed, they all had to headspace on bullet contact with the throat, as, otherwise, the extractor hook would stop the case mouths going forward far enough to headspace on the end of the chamber.
The .357 and .44 Magnums are close enough to the 30,000 psi dividing line that you may or may not see growth, depending how you load them, but I've not noticed it with H110/296. Again, you may trim for crimp consistency, but for chamber fit it doesn't seem to be needed before roll crimping has worn out the case mouths and they start to split. The straight wall case is also less prone to chamber sticking before it backs up in the chamber than a bottleneck case is, anyway. This is due to large bullet area to push back against and lack of an inside shoulder for pressure to push forward against to partially counter rearward head thrust.