Twelve-step programs (and, to some degree, their secular alternatives), pop psychology and even "real counseling" will all warn from time to time about the dangers of holding on to resentments.
But, unless it's for an addicted person early in sobriety, are all resentments "bad," or at least, "totally bad"? I say no.
I say that there can be a sort of "good resentment" that leads to a sort of "creative anger."
I can offer a few historical examples off the top of my head.
Had Mohandas Gandhi not resented the British for stooping so low as to have the salt tax on Indians, he wouldn't have thought of his Walk to the Sea, followed by his larger idea of passive resistance.
Had Martin Luther not resented Johann Tetzel's willy-nilly sale of indulgences, he might never have had the anger to share his 95 Theses and start down the road of the Reformation, even though he didn't nail them to a church door (urban legend, medieval division).
Three great revolutions, the American, French and Russian ones, started over resentments by the eventual rebels. American's turned out the best for the short and medium term, even if the long term fueled American exceptionalism. France's, while horrible for the short term, for the medium term, even, left European monarchs who kept or regained their thrones keeping at least a bit better lookout for their people and, in the long term, eventually helped drive European democracy on the Continent. Per Zhou Enlai, the book is still out on Russia's more than France's or America's, but we shall see.
We don't have to look at great moments in history, though, to see resentment leading to "creative anger."
Many ordinary people desire to "prove someone else wrong." As long as, per Hume, they let reason be the slave of the passions without letting passion obliterate reason, such resentment may well lead to creative anger that proves that other person wrong. That may be through job or personal accomplishment, reframing one's mindset or, even, with some Husserlian "bracketing" of the resentment for a while, eventually serving up a cold dish of revenge.
So, don't try to suppress, hide or smother resentment. Listen to it, then decide what to do with it and about it.