hi renae. most recipes say to wipe the chicken breasts first. This is to remove any excess moisture that might be there as it might intefere with the flavour. Chicken breasts kept in a plastic bag build up moisture really fast.
Marinated chicken is fine to be left as is. The wiping process would have been done if needed before the marinating. Hope this helps. Ive worked in delis and butcher shops and this is the normal process. Hope this helps.