There are expenses to keep the lights on. A small number of staff receive modest salaries. There's a fund for capital expenses. And if the parish manages to do more than break even, guess where the rest goes? To help the poor and disadvantaged. Parishioners are encouraged to share their money and time to support the poor in other ways, as well. There are regular collections for those causes.
I'm sure there is some level of corruption and embezzlement across the church globally, just as there is in just about any large institution, but I'd say that in terms of bringing in money, the vast majority of parishes and dioceses are just trying to get by, and to serve their communities when they can.
The image of the Catholic Church being some vast, obscenely wealthy, powerful organization is good for the Da Vinci Code but doesn't really jibe with reality. The Vatican, whose annual budget is about five times smaller than that of Cleveland, rarely has revenue that exceeds its operating expenses.
The church across the street from my house is large and I'm sure heating and upkeep is no small chunk of change. A good portion of the cars parked in the reserved row (staff) are nicer than mine, so I'm guessing the salary isn't necessarily "modest".
The story that the Church donates most of its money "to help the poor and disadvantaged" is a reassurance which is meant to paper over the fact that the Church is not a very transparent organization.
In terms of bringing in money, the vast majority of parishes and dioceses are on Church-owned land and have some sort of tax benefit or writeoff. This makes them far more stable than their surrounding community members, and somewhat ruins the image of the humble parish priest simply trying to spread the Good Word; his employer is certainly not humble in wealth.
[0] http://www.ior.va/content/dam/ior/documenti/rapporto-annuale...