Self-exclusion will be useful if someone really wants to limit themselves in gambling and will not use the money that is still in their account and will also not deposit any more money.
Apart from that, the gambler must also be able to control himself from approaching online casinos so that he does not have the urge to deposit his money again. With so many casinos that have launched and become trusted casinos, this requires seriousness from gamblers to be able to self-exclude truly.
Otherwise, it won't work well.