Sounds like there are many different approaches to trimming. In My loading book for each firearm, I have the actual neck chamber length of that firearm and prefer to trim .010 less than that dimension, as long as all of the cases clean up. I never take more than necessary and only enough to clean all the cases up. I also clean the chamber and bore often so I don't see the carbon problem that some see.
As stated in other post, I do this when my brass is new and gives me the best results. With minimum sizing, normally this is the only time I need to trim during the life of the case. generally I see very little case growth because of the sizing and the pressures I load to. A periodic check as you load is still prudent and recommended.
A dummy case in the die set is a good gauge to use when setting up your trimmer, and applying a blue die to the end of the gauge case and setting the cutter by turning it backwards will prevent you from removing any brass from the gauge case. This keeps the load very consistent unless you have to remove some of the case neck often and then thinning and neck tension may become the reason loads can change.
Also Most of the time, well sizes new cases with minimal head space will normally stay within .003 or .004 thousandths when fired the first time, and if you want to re trim then you could and start with uniform case neck lengths. After that, I rarely have to trim again.
J E CUSTOM