Just spend the money you have to spend and safe most of the rest which is left.
I do it the other way around. I set an amount I want to save. Every payday, I take that amount from my pay and save it somewhere. Then I live with what is left. If that amount is not enough, I check my expenses and remove all unnecessary expenses that I have. If that is not yet enough, then I know that I need more income or another source of income so I can survive until next payday.
Your way is also not bad, but the thing is that not everyone can manage to get another income like you so if they save the amount at first and later on they find out the remaining amount is not enough for them they start panicing because they cant find another source of income then.