The crudest way to give an example is simply to point out that if a person is subject to a probation order that requires them to do an element of community service and attend a drug treatment and testing program, if all that is over and done by five o'clock in the afternoon, what happens at night?
Probation has not traditionally been an agency that works at night. Probation hostels do. There have periodically been probation projects with car thieves, for example, that work at night or in the evening, but by and large, probation has been a daytime activity. There was no way of regulating the presence or location of an offender during the night. The idea of electronically monitored curfews—because it was originally thought of as very much a nighttime measure—was undoubtedly part of its appeal.
Here is a more creative way of adding control. The example comes from Scotland, rather than England and Wales, but it could be used this way in England and Wales as well. There was a person whose crime was to steal cars to order. He was asked by other criminals to steal a particular type of car and drive it to a particular place. I don't know quite why this person wasn't given a custodial sentence for a crime like that, but he was given a community sentence.
His electronic monitoring was used in a very creative way. Instead of being told that he had to stay indoors for 12 hours at night, what the sentence giver did was cut that 12 hours into two-hour blocks. It meant the offender couldn't travel further than he could get from his house in one hour before he had to turn around and go back. It meant he simply couldn't travel the distances that he had previously travelled to steal cars. Alongside his rehabilitation program, he was firmly restricted in the pattern of geographical activity that had enabled him to commit a particular type of crime.