One can, of course, argue both sides of this question and the answer might be different for different groups of city-dwellers. I would argue that the political machines like Boss Tweed's Tammany Hall were good for poor immigrants but bad for much of the rest of the population of the city.
Political machines essentially bought votes from the poor and immigrants. They bought the votes with city jobs, with informal welfare payments, and with other sorts of financial and in-kind help. By doing these things, they provided a great deal of support for the poor immigrants who made up so much of American cities in the late 1800s and early 1900s.
However, someone had to pay for these votes and for the corrupt practices of the political machines. Those who paid were generally the middle class. It was their tax money that was used to buy the votes. In addition, they were the ones who had to pay higher prices to make up for the bribes that businesses had to pay to machine bosses. One way or another, most of the money that was going to help the poor was coming from the pockets of the middle class.
Therefore, I would argue that the political machines helped the poor at the expense of the middle class.
Essentially, political machines were useful only to those who supported these organizations. Political machines in the 19th and 20th centuries had very distinctive purposes; they were vehicles for concentrating political power in the hands of a small group of favored politicians and securing the necessary votes to keep those politicians in power. So, one can argue that political machines helped some city dwellers but were indifferent to the plight of others.
Political machines were made up of three elements. The most important of these was the county committee (headed by a powerful boss). Some notable bosses were Richard J. Daley of Chicago, Frank Hague of Jersey City, James Michael Curley of Boston, and Tom Pendergast of Kansas City. Committee bosses had extensive fiscal control over the entire machine, and they could leverage their influence over voters to their advantage. Because of their powerful position, machine bosses wielded great influence over politicians and elected government officials.
The county committee was supported by precinct leaders who were each responsible for hundreds of families under their jurisdiction. These leaders were called precinct captains, and their main focus was to ensure that impoverished families in their care received social service aid, jobs, and legal expertise (when necessary). The last element of the political machine consisted of party loyalists. These loyalists supported the machine with their money and time; many received government jobs through the intercession of government officials beholden to the machine. In return, these loyalists had to hand over 10% of their weekly incomes to the county committee.
During elections, party loyalists worked to get out the vote; they handed out leaflets and brought neighbors and family members to voting stations. One of the most famous political machines in the 19th century was Tammany Hall in New York City. Tammany originally championed the rights of "pure" or indigenous Americans. However, it later admitted Irish immigrants. The Irish were a resourceful and tenacious people, and as time progressed, their influence grew, making Tammany Hall an Irish political machine.
Tammany Hall worked to secure the rights of the Irish immigrant working class, but it largely ignored the needs of other immigrant groups. Meanwhile, bosses like Frank Hague of Jersey City leveraged political influence over the working classes for personal aggrandizement. So, we can say that political machines worked to benefit the lives of only some city dwellers: certain immigrant groups and the working classes. These machines also benefited committee bosses, participating politicians, government officials, and party loyalists. Many of the voters that kept these political machines in power were destitute, marginalized members of society. They had no other choice but to trust that these political machines would serve them well.
Bosses like Frank Hague worked tirelessly to secure support from the larger community. Hague donated to veterans' groups and church organizations; when elections came, these organizations were instrumental in getting out the vote. Hague also cleverly courted the mother's vote by clamping down hard on gambling dens and prostitution rings. Last, but not least, through sheer political will, he brought the 2,000 bed Jersey City Medical Center into being. It provided free medical care to many impoverished Jersey City residents. The medical center cost $3 million annually to run, and Hague paid for it by instituting higher taxes.
Again, it can be seen that political machines benefited some city dwellers, but they did so at the expense of those who had to foot the bill. Additionally, political machines were used to contain power in the hands of a corrupt few. Some immigrant groups were also marginalized and kept out from the circle of influence altogether.