Excessive case length does effect accuracy. Cases grow when fired and reloaded and MUST be trimmed to the same length.
I have no ideal why one wouldn't want to trim the cases.
Lee's little case trimmer are cheap and accurate, easy to use.
Maybe it's just me, but my accuracy is worth the few bucks it takes to trim the cases.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071