Originally posted by Pentaxor why would he still need a soft focus filter when you can do that during post-processing.
With that statement, several assumptions are made:
1. OP only wishes to shoot digital and will never shoot film.
2. That OP owns expensive photo editing software such as photoshop.
3. That OP has the computer with the grunt to run such software smoothly and a colour calibrated monitor.
4. That OP has the skillsets to do the tasks required.
5. That said tasks are repeatable processes, instead of requiring an artistry and judgement.
6. That OP has the time and inclination to perform said creative tasks repetitively.
Those assumptions may be true in entirety or part varying from person to person, however they still remain risks that the resultant work will not match the expectations of the person that commissioned the portrait. The risks can be avoided to quite some degree by using a "soft" lens or a soft filter.