The OP and many posters know the following, but the more casual reader should be aware of a few considerations.
Unlike a FFP optic, with a SFP scope, the thickness of the reticle doesn't change as magnification is turned up on a variable magnification scope. A fine crosshair reticle is usually preferred by paper target shooters who shoot at known distances, such as in bench shooting, because it won't block out a small point of aim. A crosshair that is wider than a bullet hole or two is less desirable for shooters who want to set the center of the reticle as precisely as possible. At prescribed distances such as 50 or 100 yards, SFP scopes are sighted for that range and it's not expected to shoot at other distances without making scope adjustments.
As noted by Longstud in post #5 FFP scopes are useful when shooting at varying distances and using the scope for factoring in "dope" such as bullet drop and wind drift, such as in CRPS-style shooting events. To illustrate, the mil or MOA points or lines on the reticle will be accurate throughout the magnification range of the scope. With SFP scopes, the mil/MOA points are valid at one magnification level only, with some calculations required for multiples of that level. Whether to chose a FFP or SFP scope will depend largely on the most common use of the rifle and glass.
It's important to keep in mind a few things with regard to high power scopes, FFP or SFP, and movement caused by external factors whether they be heartbeat or breathing or vibration from the bench or rest. The key is always stability. If a sight picture moves because of the bench, then the bench and rest or bipod is not stable enough. Same for heartbeat. This is often a more significant problem with lighter rifles that need to be held more tightly than heavier ones.
A stable bench and rest should allow the use of high power scopes without movement in the sight picture. The thing is that if there is movement with a high magnification scope, that movement itself doesn't disappear with a lower magnification optic. It's still there. The difference is that while the shooter notices it less or not at all and finds that reassuring, the rifle is still moving just the same and that has a negative impact on the target downrange.