The only systematic test results I've ever seen (Phil Davis) indicate that response of various films vary perhaps randomly to a long pre-wet of five minutes; some gained contrast, some lost contrast, some gained speed and some lost speed. Compensation of development time or EI for a long prewet (as recommended by Jobo) isn't predictable by any common amount and can be determined only by testing your materials.(posted 8852 days ago)Phil also found that a short prewet (one minute) has negligible effects on EI or CI.
He didn't address other reasons given for a prewet, such as the prevention of airbells or to promote evenness.
I've experienced airbells when developing rollfilm in a Jobo rotary processor without the use of a prewet; oddly enough, this was with Xtol, a developer for which Jobo specifically recommends _against_ using a prewet. A one-minute prewet solved the problem with no unwanted effects.
Uneven development is a symptom of insufficient agitation or non-random agitation movements, usually during the first 30 seconds to one minute of development. A prewet will not cure any of these problems.
According to Ilford, their films incorporate a wetting agent in the emulsion and a prewet should _not_ be used because it'll wash out the wetting agent and may cause some of the problems the prewet is expected to prevent. I have no idea about other brand films.
So you need to make the decision based on the results you're getting, not on "common wisdom" aka "old wives tales."
If you're getting airbells then a short prewet may prevent them.
If you're getting uneven development, modify your agitation techniques.
If you don't have a problem, don't fix it.