Now granted there are a few talented experienced folk that can reach optimization by ear, but many/most have not experienced “optimum”. @atmasphere seems to be alluding that there’s much more performance that can be wrung out of your existing cartridge if it is not yet optimized.This. +1
Due to the crude adjustments or complete lack of adjustments on many arms, optimizing the cartridge is very difficult if not impossible! If ever there were things that cause analog to be problematic as opposed to digital, this is certainly one of the big ones. Flip that coin over- if you have an arm where every adjustment is easy, and add to that no arm tube resonance and no chatter in the bearings then you can get the cartridge to perform.
I can give many examples but a small one is this: If you wish to optimize VTA using an SME5 it is done by raising the arm. But first you have to use a tool to loosen the arm pillar from the base. Then you can use the threaded rod on the left side of the arm that bears against the mounting plate, thus raising the arm. Did you go too high? backing up the adjuster does not cause the arm to sink- you have to push it down. Hint: Apply a dot of white paint to the top knurled knob (which should be several times larger) so you can count the number of turns you've set up... watch it though- when you loosen the arm pillar, the arm can rotate with respect to its base. Point is- its tricky. With the arm I have now there are two graduated scales and I can adjust the VTA on the fly. This design has been copied by a lot of arm manufacturers but SME isn't one of them.
Arm tube resonance is the simple fact that the arm tube is made of something, and that something can vibrate. It should be damped so it can be neutral. Most arms have nothing in this regard- some do. Now if your arm tube is editorializing while you are trying to play music, will your cartridge perform the way it should? Of course not. If the bearings in the arm chatter because they are set slightly loose, same thing. If the bearings are in the plane of the arm tube rather than the LP surface, same thing.
I master LPs. I know what the master tapes sound like, and how LPs produced thusly are supposed to sound. I heartily recommend to anyone to do something similar- at the very least get a nice set of microphones and record something you can stand to listen to and get it mastered to LP. Then you will have a reference. This is invaluable!
The bottom line is as quoted above.