JV, I think you are looking at it in a simplistic manner; no aircraft is `Murphy-proof`,and especially where flying controls,be they `primary,or secondary`,whether operated by a `suitable system of cables,rods,levers,hyd.jacks or `wiggly amps` thru an autopilot. There is always the possibility that it can be wrong.
There are many of your `secondary controls` which could be described as primary,ie wing-sweep(could spoil your whole day if only one wing moved,or they moved without input.Similarly `spoilers` are used on some aircraft as `Direct Lift Control` in certain configurations. Spoilers/airbrakes are also linked in some aircraft to be an automatic Mach/IAS limiting device,opening as the airspeed reaches the limit,in a predictable manner.If they are not checked properly,and open asymmetrically/too fast/slow,it can lead to making everyones eyes water,and damage can occur. I can certainly attest to many events as a TP and MTP of having to bring an aircraft back to the `gingerbeers`,with control/rigging problems, and I`m sure JF and LCV have done the same,especially when the aircraft is just `out from maintenance`.
It is also my experience that an MCF/MTF prior to going into the shed is valuable if done by the test crew,and all the `snags/deficiencies are noted then.
Last point,take the engineers on the test flight....