[amamnn]

For shooters who can take advantage of the tighter tolerances of custom built rifle barrels--the ideal is to have all the cases be of the same shoulder datum length and also of the same trim length which presupposes a set neck length which results in the same bearing surface and bullet release. For BR shooters, the equipment and time and money invested in determining these data along with others, are worth the blood and treasure, so to speak.
The Lee trimmers will do an adequate job for most of the rest of us. They trim to "Lee length" which is somewhere between the min and max recommended lengths. If you have set up your sizing die to match your chamber fairly well, you will not need to worry about it. A case that is not worked too hard will not need to be trimmed all that often--this is especially true of cases fired in bolt action chambers, but it is also true of direct gas impingement action rifles, though you may have to trim a bit more often.