Adjusting pole pieces is definitely worth doing (humbuckers). Contrary to what most say; (based on testing) does not really give out more output, rather emphasizing one coil sound prominent over the other coil. You may get more apparent drive/volume/mids/treble BUT at the cost of clarity and tone loss (no good). You'll get a distorted sound but not a clean tight overdrive sound.
Basically adjustments up/down alters the inductance along the length of the coil and also the "magnetic balance/flux lines" over the whole guitar body. The character of any pickup is inherent in the windings/wire type/bobbin type and by how much wound. The Goal here is to get the most out of your pickup interms of Clarity, resonance, low noise, harmonics, etc.
Sometimes especially chords don't sound so crisp even if tuned perfect, even if intonation is right. Sometimes you find pickup combinations sound abit off (especially to get that quack-out-of-phase vintage sound)...and finally you wonder why on Monday, the guitar sounds good but Wednesday it sounds abit rubbish in tone.
The good news is that there is one pattern that works really well. But have never seen it on any pickup over the last 30 years or any other blogs/forums. It's just TOO MUCH hassle for manufacturers to do this. The pattern that works, balances out the tone/dynamics and clarity with the "Slug" pole piece coil. It can also be used on single coils too. Every time you add a pickup to your guitar, it makes the task of clarity a little more complex because more magnetic disturbance anomalies can exists.
Make sure all your pickups are the same height (on the same axis)(top of plastic bobbins)..approx 2.73 mm from strings.
Aim for this pattern 5 6 1 1 4 4 corresponds to E A D G B E
Now with Overdrive; Play each string one at a time on the 7th Fret - Listen out for a slight flutter-wavering note [ It should NOT waver - adjust very slightly up/down to get a flat-line tone/note ]
If you want to fine tune this clarity, and you have a good ear...do the same on the 19th Fret (even smaller- annoying adjustments)
The chat about neck radius, string gauge, bridge intonation, pickup output, changing tones and what-have-you do matter somewhat, but are mis-leading ...they are NOT major factors really. What the pole piece adjustment does is create balance inside the adjusted coil and in combination with the fixed slug pole coils in humbuckers (Longitudinal & Lateral magnetic flux lines). You are also adjusting the overall inductance and how it is distributed. When all the pickups are adjusted...They ALSO blend well together.
Cheers & Enjoy !
Before adjusting the pole pieces and especially if you're new to this; it's better to only have one bridge humbucker in your guitar then add all the the other pickups one by one.
The Ultimate test/biggest impact on tonal quality is when you select two pickups out-of-phase with each other, this method proves perfect.
9/10 times the middle pickup HSH configuration mucks everything up. So adjust it's pole pieces manually if need be. Another good tip is once this is done, cover the middle coil (only) pole pieces with only one layer of PVC electrical tape (over the 4 inner poles). The sound will be less harsh and quite smooth and will balance better with the other pickups. I prefer Alnico magnet for the middle single coil pickup, ceramics can be too rough/overpowering sound.
It will accentuate one string more than another if that is your desired sound. Once you've adjusted the whole pickup to its desired height remember raising individual pole pieces will quickly take them into the magnetic drag area, so do it in small increments.
Ultimately use your ear, adjust to your taste. And the guy who said it would affect the 'magnetic balance/flux lines' over the whole guitar body was talking a lot of nonsense.