Spokespersons improve sponsors mood, and, to a much smaller degree, supporter mood.
Sponsors are happier and pay your club more money if they have spokespersons they can talk/listen to. Research in the newbie (English) conference suggests that optimal number of spokespersons is around 1 per 250 fans. But it might be useful to temporarily hire more than optimal at the start of the season to recover sponsor mood quicker from the reset.
Warning: More than 10 spokepersons will make your sponsors mood drop.