In Douglas Blackmon's Pulitzer Prize-winning book Slavery by Another Name: The Re-Enslavement of Black Americans from the Civil War to World War II, the author richly documents the harsh use of African American slaves in mining and the production of steel in the US South, especially in Alabama, during the period before emancipation. Thousands of African Americans, including prison inmates and people who had been wrongly convicted of real or sham crimes, continued to labor in near or actual servitude in those industries, among others, after the Civil War and well into the twentieth century.
Blackmon, Douglas A. Slavery by Another Name: The Re-Enslavement of Black Americans from the Civil War to World War II. Knopf Doubleday Publishing Group, 2008.
In New England, enslaved populations tended to be more diversified in their tasks. There are a number of reasons for this, but the two largest are A) the agricultural differences of the North and B) the more urban nature of enslavement here.
DesRochers completed the first real comprehensive study we have of slave employment by examining slave sale ads for Boston between 1704 and 1781. These still aren't an entirely perfect source to compare to New England or even Massachusetts as a whole, as Boston enslaved population (apx. 1200) dwarfs the nearest competitor by the 1740s (Salem, MA, apx. 83).
The article is accessible for free on JSTOR, so I won't repeat everything here (categories break down to individual occupations). But there are a few highlights worth mention.
Male slave occupations break down to:
36.3% General laborers (dockworkers, etc.)
27% to Household labor (servants, cooks, coachman, etc.)
19.1% Crafts, Trades, and Skills Labor (tailors, cooper, carpenter, sailors, etc.) and
17.6% Rural Labor (Farming, Husbandry, etc.)
Female Occupations broke down to:
24.7% General Labor (Indoor and Outdoor)
71% Household Labor (Cooking, Sewing, Spinning, etc.)
4.3% Rural Labor
Another point worth mentioning here is that unlike the South, where slave ownership was largely an upper-class phenomenon due to price, slave ownership in New England tended to be a goal for many in the working and middle class. Slave labor would often be used to directly replace at least a portion of the labor of the master, allow him time to devote to other pursuits. This may be something a small as increasing their output to increase profits, or devoting themselves to new professions such as law, medicine, or trade. In effect, slave-ownership allowed for many opportunities to increase ones social and economic standing.
This is another reason why studies of slavery and the slave trade in New England have forced some major, and unpopular, public discussions about the legacies of that money and how much it benefited the North. Harvard Law School was founded by an endowment from a slaveholder and trader. The founding endowment for the Boston Public Library too came from a slaveholder. Boston's Faneuil Hall was built, and is named for, a slave trading family. The investments which gave rise to Massachusetts' bustling textile industry also trace back to slavery, the slave trade, and the West Indies trade (as well as other slave-free trades, such as the East Indies).
In short the benefits of slavery were more than simply monetary, and have had a long lasting impact on New England.