To get the best possible answer, you may want to clarify your question. It is not clear from whose perspective we are to look at this. In other words, to whom is prostitution supposed to be a financial benefit? Let us look at some possibilities.
First, it is possible that prostitution is financially beneficial to the prostitute. This becomes more and more plausible as we move up the hierarchy of prostitutes away from the streetwalkers. For “higher level” prostitutes in particular, prostitution can be a much better way to make money than any other option available. It is not easy to find a legitimate job at which one can make $50 or $100 per hour.
Second, it is likely that prostitution is financially beneficial to the pimp or to the escort service. These people presumably have relatively little in the way of overhead expenses. If they can extract a decent percentage of the prostitute’s fee, they can be profitable given the fact that their expenses will often be rather low.
Finally, we can imagine that prostitution could be financially beneficial for the community as a whole or for a district within a community. This is particularly true of “destinations.” It may be the case that some people will travel to a place like Las Vegas with the assumption that prostitution will be one option available to them as “entertainment.” The existence of prostitution, then, might be one factor that helps draw people to a city. While there, they will spend money on other things, thus helping the overall economy.