Instead of taxing the small citizen that is just scraping by paying their bills. By collecting this tax it will ultimately bring in another stream of revenue that the government can put toward reducing the deficit. Some banks were bailed out at one point so this is a valid way to repay the government for the help that was exteded to them.
Yes, it will help reduce the deficit by adding another revenue stream for the government. Bank taxes will help boost the economy, as well as continue to keep some form of regulation on banks. It is important to consider all possibilities when thinking about how to reduce the national deficit, and the US bank tax is a perfect example of how to assist.