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.
Basially 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 ONLY one pattern that works. But have never seen it on any pickup over the last 30 years or any other blogs/forums. It's just TOO MUCH hastle 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. Alot of HSH pickup configuration will never sound hyper clear, mainly because the middle single coil has fixed-set pole pieces, and that throws everything out. 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 6mm from strings.
E A D G B E = 5 4 3 2 0 1 (these are the relative height adjustments with 0 = flush with bobbin) - Try adjusting screws at 30 degree intervals. YEP, that's right the B-string pole piece is flush with the bobbin top.
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)
BTW: I've tried lots of patterns, believe me...even vintage stagger ones - Nice in theory but not clear/not tight/very jangly also. Yes you can get some interesting sound tones but never really defined and clear tones across ALL the strings and on every fret.
The chat about neck radius, string gauge, bridge intontation, 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 !
This method I mentioned above, is my own development. I've done this on Ibanez, Fender, Jackson, Aria Pros, Kramers, semi-hollow and crappy guitars...It absolutely works a treat.
In addition I must stress that ALL the pickups are perpendicular to the guitar body and NOT angled at all. For this reason I do not use angled pickup rings (as found on 90% of most guitars). If you have a scratchplate (fine) or use flat pickup rings/surrounds (if you can find them !!
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.
All your pickups must be adjusted to be exactly the same height and level with each other WITHIN the 1MM !!!!(top of bobbin plastic to guitar body) so that all the magnets are lined up on the same plane and the magnetic flux lines will be better also.
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.
p.s. I don't agree with the assumption that frequencies cluster around the middle "C" note approx 256Hz to 278Hz ...It depends on the Inductance and capacitance characteristics of each coil.