According to Fandom wiki, ticks deal pierce damage when attached. Broods also deal pierce damage (as much as 60 in fact, not to be ignored). In addition to those, root harnesk can also help with avoiding a sudden death from sneaky dvergr rogue you managed to upset. I played through entirety of mistlands with root harnesk. You don't need it to succeed, how much use you find for it depends how you fight and which enemies are more trouble for you.