It is important to keep bottle neck cases trimmed to within max SAAMI specification to prevent pinching in the throat, thus avoiding excessive pressure issues.
As for straight walled brass, auto loading cases that head space off the case mouth can in some instances grow longer than what will allow the round to chamber deep enough and create issues related to battery.
Rimmed cases, or those that are commonly operated through a revolver need to be trimmed to same lengths to assure consistent crimping. But this can also be true when working with auto loading type cases, if some are excessively longer than what the crimp die is set up for, an issue of over crimping could result in loss of neck tension, buckling of the case, and deformed bullets. I often see posts in which reloaders are struggling with problems that I think are obvious indications that inconsistencies in brass length is the major contributor.
Many who reload don't feel it is necessary to trim straight walled brass. I do not agree with this and maintain all my brass to within SAAMI spec and to same lengths. As a result, I've never had problems with excessive crimps or lack of necessary crimp, battery issues, FTF's, and so on. There are very good reasons why all brass should be maintained accordingly, and if it is supported by a SAAMI specification, then it is necessary in my opinion.
GS