The helicopter stability section has 3 numbers to define that are very important.
low_realism_stability_scale = 1.0, 1.0, 1.0 //Pitch , Bank, Yaw Scalars on Stability in Low Realism Settings
Before getting into specifics, let's generally lay out what these numbers do. Think of them as GLOBAL stability modifiers that affect the helicopter flight model along the 3 primary axes. As far as how flight simulator applies them to the flight model...think of them as being phrased like this:
Given a flight simulator where the general realism slider has been set to the lowest setting (Aircraft->Realism menu), how much additional stability should be imparted with respect to each axis of the aircraft.
By default these numbers are VERY HIGH, which leads to a sensation in flight simulator that can be described as "flying on rails". Control inputs will feel very rigid, and moments of inertia will lose their fluidity. These parameters where probably geared at attempting to make the helicopter flight model more accessible to new users. While in reality, because of the negative effect it can have on control responsiveness, it can actually make it harder for a new user to learn to fly the helicopter successfully.
For FS9 The default values of 1.0 used for the default Bell 206 are rigid, but workable, for most new users (most users do not know these exist). Numbers in the area of .65 for each axis would supply a slightly more realistic and fluid control response.
For FSX It would appear that the global baseline for these numbers has somehow been altered in FSX. Such that 1.0 is much more rigid (ie. more stable) in FSX than it was in FS9. This was easily noticed by most helicopter developers upon the release of FSX. I have found that a number around .60 in FSX reflects what used to be observed in FS9 using a number around 1.0 - so as a matter of course, nearly all of my FSX helicopters receive this adjustment before any other flight dynamics adjustments begin.
In addition to generally setting these numbers values that you generally enjoy, these can also be manipulated to create ever more responsive and challenging-to-fly aircraft. Depending on how the stability and inertia of a flight simulator aircraft turns out after tweaking and tuning other flight dynamics characteristics, sometimes these numbers can end up far lower. For example, it is not unusual for aircraft that I modify for FSX to end up with stability numbers in the .30-.45 range. Sometimes the yaw axis will receive a slightly higher value to help counteract the fish-tailing that the helicopter flight model is prone to at high speeds. However, adjusting the stability number alone is not an effective way to solve the problem of fish tailing.
The Flight Simulator SDK may sometimes note this as being the only useful item for Bell 206 based helicopters in the aircraft.cfg file. Considering that weight and balance, station loads, moments of inertia, fuel storage and location, and a variety of other electrical and systems configuration in this file can be used on the helicopter, I'm not sure why they say this.
The R22 and EH101 helicopters have additional helicopter sections in the aircraft.cfg - as they do indeed get the majority of their flight dynamics information from this file. Good in that this file is easier to work with than the .air file, but bad in that there are only a few variables that can be adjusted and the behaviors are rather "fixed". I add this note to warn you that it is not uncommon to find a bell-206 based helicopter that has an aircraft.cfg file that includes the helicopter entries from either the R22 or EH101 aircraft.cfg file added to it by another developer. Despite their wishful thinking...these entries will be ignored by the Bell 206 flight model. They are for the R22 and EH101 flight models only.