If you tray develop sheet film in batches, you need to pre-soak to keep the film from sticking together in the developer. If you use a tank or develop single sheets, there's no real need. If you want to get rid of the anti-halation dyes before developing you need to pre-soak, but that's more of a personal aesthetic than a necessity.
With rotary processing, it is often a good idea to pre-soak to get the temperature stabilized and to help with evenness of development (the danger being streaking from the film not being completely covered fast enough by the developer when pouring it in.
I tray develop in batches and pre-soak all my film (TMX, TMY, 320Tri-X, Bergger, etc.). There's no real downside to pre-soaking as long as the pre-soak is long enough to completely saturate the emulsion. Care needs to be taken to soak films with surfactant incorporated in the emulsion. I'm not sure if Ilford films still have (or ever did have) that, but Kodak films don't. Three minutes with agitation is long enough.
Be sure to introduce the sheets into the water bath one-at-a-time and leave 10-15 seconds between sheets so they don't stick together. If they do stick, simply extend the soak and gently work them apart. No damage is done if this happens in the water bath (as opposed to the developer!).
Best,
Doremus