100Hz (or even 50Hz) tuning would make sense for HF but not VHF/UHF.
I admit that it is a pretty small step for the typical scanner.
My reasonig was based on something I found when using an Icom R2500 that also had the P25 digital card in it.
I found a few VHF single channel VHF users that the R2500 (or Uniden or GRE scanners) would not decode their P25 signals very well.
So I started playing with the R2500 one day as it has a super low tuning step like 1 hertz. I set the R2500 into P25 mode and tuned one of the stations that the 2500 and the scanner had a hard time with.
I set the tuning step as low as it would go but ended up back around 100Hz. I then started tuning off the channels center frequency and I'll be darned if the R2500 did not start decoding the P25 signal perfectly.
I think I found the sweet spot just under 1kHz from center frequency. I then tried that on another of the single channel P25 signals here and same thing, it started decoding the signals just fine. But I could not do this with any of the scanners because they do not allow such a fine tuning step.
I then setup a laptop attached to an Icom R7000 and an R9000 and used DSD from those radios. Sure enough, I had the same good results when I'd tune the R9000 off center frequency to match what I'd tried with the R2500.
I then tried the R7000 which has a 100 Hz step and it also allowed DSD to tune the P25 signals that the scanners will not.
So that was my reasoning for wanting a low tuning step like that as I'm failry certain a Uniden or GRE would also decode those same signals if I could offset them just under 1 kHz. A buddy at a communications shop used a service monitor on the signals that the scanner would not decode to see if the signals were off frequency but they were both dead on and both had perfect modulation.
One day I plan on moving the frequency of the PSR600 by the same amount and see if it will decode the signals. My guess is that it will.
I have the service manual for the radioshack version of the PSR600 and it is an easy to make adjustment but I've just not had the time to try it yet.
Right now, I can use my R2500 to decode the two stations I tested this on but I program the frequencies 800 Hz plus or minus the true center frequency and it decodes them both just fine. I forget and would need to fire up the R2500 to see if it was 800 higher or lower.
My point is that if you can clean up a P25 signal by using small steps off the true center frequency, I'd love to have this fine tune ability in a scanner.
I have not tested the theory on a multipath distortion problem site yet but I plan on also doing that as well. It sure works for single frequency P25 reception and it would be great if it worked on a trunked P25 site as well.
If it does, then darn right, I want a small tuning step so I can manually fine tune the systems that come in so badly now.