There would be a marginal improvement if it became mandatory, as opposed to no improvement. So it would be a small step in the right direction.
Legislation, beyond being immediately effective, also sets a goal for the police and courts. I think that by putting their stamp on it that one should be tougher on serious criminals, this will do more than merely ensure that 200 or 300 more people are not allowed out to murder, rape, or kill. And 200 or 300 who are not out is clearly an advantage.