Just recently bought an stc-1000 unit, and for my first brew, a 'pilsner' kit, i have the probe in the wort.
My thinking was that as the brew produces heat as it ferments, the brew will be warmer than the surrounding air as it will eb insulated by the FV. Therefore, controlling the surrounding temp does not necessarily mean controlling the wort temp.
Other people disagree with this, but I can't rememebr why off the top of my head.