1. Keep track of my actual spending..
2. It helps me keep and maintain a threshold in times of long loosing streak - i will explain further..
Since everyone has a different approach to their respective gambling activity, if you found that useful and helpful for you in the long-run, then you can keep up with that. Might not work for everybody but good to see that it gives you an advantage, especially in tracking your actual spending in gambling.
In my case personally, I don't really the kind of gambler that want to track my actual spending. Not that I don't care about losing money but it's just that it's not a big deal for me to track it as that's not my gambling way. When I lose, move on and will start as new on my next gambling session only taking care with the win on that particular session.
With stable coin, keeping a clean sheet is possible as $1 loss will always be $1, while a $2 win will always be $2 since stable coins do not show any significant increase or decrease in their price except in times of crises, which is not something that happens frequently..
The alternative: play with fiat online casino, and your number 1 and 2 reasons will now be covered.
Kidding aside, since we talk about crypto-gambling, using stablecoin is really useful, as you say, to somehow won't be able to reach your limit threshold.
But also remember, we are also talking about gambling here and regardless if you are using stablecoin or not, can you really resist the temptation to continue gambling when you are currently, for let's say, already reached the limit of your own threshold or already win a big money in the process? It's difficult and hard to take a break in that situation.