Hi,
First thing first, every single refrigeration system is unique and different! TEV's are mass produced!
That alone tells you why your superheat needs to be checked and adjusted accordingly. Any decent comissioning engineer will know exactly when the operating conditions are stable enough to gauge the superheat and when to adjust.
In todays world where keeping energy consumption to a minimum, getting the most out of your evaporator is paramount. If you can control a relatively small superheat(6'C) and raise the evaporating pressure as a result, energy savings are achieved and compressor running hours can be reduced.

Regards

Chopper