House arrest/electronic surveillance is based on the flawed, punishment/rehabilitation model of dealing with criminals. Simply put, incarceration is supposed to be punishing which encourages the criminal to avoid further criminal acts while interupting criminal behaviors and allowing an opportunity for reform. Because of budget constraints, the lowest risk (supposedly) criminals are allowed to do their time at home. This supposedly accomplishes the dual goals of being punishing, so as to influence future decisions as to engage in crime or not and interupt various behaviors that allow reform. For example, hanging out with gang members or going out scoring drugs are difficult to accomplish while under house arrest.
Note that the entire system, from top to bottom is a complete and dismal failure. There is plenty of evidence to suggest that the punishment/rehabilitation model is a fraudulent construct (ie the people implementing never had any intention of succeeding).
A better model, and one for which many legislative bodies are forcing the judiciary to adopt is the goal of protecting the public. That's the impetus behind 3 strikes your out, mandatory minimum sentencing, and LIMITING USE OF HOUSE ARREST in favor of jail. Simply put, a criminal in prison cannot victimize anyone....except other criminals, which they do with great agressiveness, I might add. This is what leads the push for more SuperMax style of prisons where contact with other prisoners is severely curtailed.
Also, I would like to add that the part of your question, "what does the person on house arrest have to gain" is COMPLETELY inappropriate and a leading cause of most of the problems in the criminal justice system. Prison is not welfare. It does not exist to meet the needs of criminals. Rather, it exists to attempt to deal with these people as a major problem for society. Mostly, this is accomplished by seperating the problem person from society. The person's needs are irrelevant. Meeting them has zero effect on the goal of stopping and reducing crime. This is not a debateble point but rather the result of careful measurement of the problem over an extended period of time. Criminals have needs. Prison, the police, the courts are not where they should get those needs met....ever.