Changing the offset might have a small effect on the UR you get on the map. The bigger the change, the higher the effect, since it changes the feedback you get; small changes, like 5ms, do not really change audio feedback (because of the buffer system the sound engine the game uses), and thus any perceived difference in the audial feedback is just placebo.
You need to have a low UR in the first place to know precisely how to change the offset, in order to maximize the accuracy percentage you get on the map.
For example, if you get an UR of around ~90 (9ms of standard deviation), and average early/late hit errors of -5ms/10ms, you can be confident you would get better accuracy on the map if you changed the local offset in the map by around (-5ms+10ms) * 1.4 ~= 7ms; but if the UR is way higher than that, with the same difference between early and late average offsets, then the difference would likely mostly be caused by random variation from the imprecise hits rather than an offset that is really wrong and should be changed.
Most songs in the game have a constant BPM with no metronome resets. For improving accuracy on those maps, indirectly improving your UR, playing by an internal metronome that is undisturbed by changes in the music or notes (as long as they aren't changes in tempo or metronome resets, not present in most maps), instead of having to rely on constant feedback from the audio or the graphics (that feedback would be used in order to notify you when you went astray, but if you are aiming to get good accuracy, you shouldn't go astray at all and thus you don't need to pay attention to them), helps; that internal metronome is calibrated by paying attention to the music before you start pressing buttons (this is a reason it is harder to sightread maps that begin at the same time as the first instruments in the music with high accuracy is harder). In music with more complex rhythm, using the music to sense when to adjust your internal metronome is more important (unless you develop a very accurate visual reading, in which case you can use the timing on when the notes appear on the screen to precisely adjust your internal metronome).
Also, pressing the buttons firmly (but without straining your hands, making them tired) makes your inputs more consistent.