Re: FFP why ?
Ranging is only one reason to use them...
The reticles have value, every bit the value a turret has, but only on one power with a SFP scope... with a FFP scope you can use that value to engage targets without having to come off the rifle to engage the turrets.
For example, wind holds, I use the reticle not the turrets, winds change to often to try and dial the change, using the reticle allows you to be dynamic in those holds.
Moving targets, I use the reticle to engage movers, which depending on direction of both the mover and the wind may require a different hold for different directions. The reticle must be valid and with some scopes, like a 20X the FOV is too narrow to use, so you want to dial down. Having the ability to have valid holds at lower power is important.
Night vision, or lower light situations, less magnification make it easier to see in such conditions, so again, valid holds.
You can use this for both windage and elevation, having a FFP scope ensure your holds are valid.
Ranging is the last thing I do with a reticle. In fact ranging is easier on a higher power. So it's not as important. However holds are...