I had a number of discussions with Ilford (on the IlfoPro forum) and while they do not recommend a pre-soak they say it does no harm but extends the development time.

The ilford emulsions contain an agent that allows the developer to be absorbed quickly and reduces development time. The presoak removes this agent. So for rotary processing they recomend using the small-tank developing time.

I have always used a presoak whether using a small-tank or my Jobo, and have never had any issues. But then again using large tank development for sheet film I have never used a presoak and still worked.

- Mike