Saving is part of my life and I have never seen it as an impossible task that needs to be done with efforts.
It should be good for you if you have multiple sources of income, but I don't know if you need to maintain a percentage of that amount each month. Even if saving is recommended, but I don't think it's necessary to have a special percentage in doing so and just do how many you can save.
If you insist on saving a certain amount each month then you may run into problems when your source of income dries up for one reason or another. This will definitely give you a lot of responsibility so that you can or should reduce your daily and monthly needs to get the percentage that you set. You can do it, but your method cannot adopted for other users.
But if we don't have a specific goal, it makes us more lethargic and lazy. It is better to give a specific number because we will be more disciplined with ourselves to achieve that goal. You are right that we apply it will make us more stressed in life but that savings will come in handy in your emergency. I also like to impose a specific number when it comes to saving and investing, which will help me reach my goal quickly rather than dragging on and never completing it.