I am against any kind of absolute restrictions. If you like something, first and foremost you need to learn how to coexist with it, not try to cut it out of your life.
Different opinion, but whatever works for one should be the one they adopt.
The disadvantage of not cutting down completely what I feel is that the chance of relapsing back into addiction is very close. Because discipline is something that is lacking largely among most gamblers.
From time to time they will get the urge to gamble again. Slow cutting down might be a good option at that time. Often moving away from the scene and going to a different place, engaging with stuff other than the regular can break the habits.