Bad advice to a new reloaderI have ran many cases .020" short of what trim length was and there was no issue in doing so.
Accuracy may have suffered but until you prep the snot out of the cases and sort and weigh and set powder charges to the exact granual you probably will not notice the shorter trim length.
Unless you crimp of course.
I intentionally cut some .308 way short so i did not have to trim for 20+ reloads. they still shot sub moa.
That is a different story though..
After you reload for some time you will discover what makes the most differences for you and your rifles.