This comes up every now and again, i have yet to have seen any manufacturer instructions for any C-41 (or e-6 for that matter) that call for pre soaking, i know of no commercial machine that presoaks either.
Why do people do this?

Some years ago, someone taught me how to make perfect rice - they said: "read and follow the instructions".

I guess thats good advice to anything in life that comes with a manual.