In chapters 6 and 7 which vices are considered useful and advisable? Why does Machiavelli recommend them?

Machiavelli reccomends that a prince shouldn't avoid vices like cruelty and dishonesty as long as the vices directly benefit the state.

"What Machiavelli seems to object to is careless spending; better for a prince to be thought a “miser,” for his parsimony will enable him to live on his income, not raise taxes, and defend against enemies, all of which will in turn earn him greater respect in the long run. “Hence a prince who prefers not to rob his subjects,” Machiavelli writes, “who wants to be able to defend himself, who wants to avoid poverty and contempt, and who doesn’t want to become a plunderer, should not mind in the least if people consider him a miser; this is simply one of the vices that enable him to reign.”

"If a prince needs to indulge a vice to save his state, so be it. “For if you look at matters carefully,” Machiavelli writes, “you will see that something resembling virtue, if you follow it, may be your ruin, while something resembling vice will lead, if you follow it, to your security and well-being.” One might compare this argument to the thrust of Chapter XIII, “On Those Who Have Become Princes By Crime,” which measures when and to what extent a prince’s cruelty can be justified. Machiavelli is arguing something far more complex than a call to disregard morality. His example of the generous prince begins as a seemingly hard-lined argument and emerges as a humanist consideration of the faults of man. A prince should not be miserly just for the sake of it; miserliness, by resulting in the safeguarding of funds and greater financial security, winds up helping the people in quite direct ways. It is up to the prince to see beyond short-run desires and superficial appearances and to not give away money he cannot afford to spend just to put on a lovable face and to curry favor, but instead to weather the occasional criticism and plan for the future."