My experience is whenever I input perfectly accurate winds into descent forecast page the plane tend to slow down below Econ descent speed to the point where thrust is added. Entering altitudes for TAI also seem to have relatively little relevance, in my humble opinion. Personally I normally leave the page empty apart from the destination QNH, which if very high or low can affect the profile significantly.
Where I go we are mostly on vectors from very early on which make V/S or Level Change more appropriate. Whenever not following the magenta line (LNAV) I go out of VNAV, even though it can be used if the vector somewhat parallels the magenta. VNAV can be a fantastic tool for optimizing continuous descents but i have also seen it done pretty weird calculations so running a mental gross error check is a good idea.