It is one of very first steps to do in gambling but it is very vital for your financial management in general and your risk management for your gambling activities and your gambling fund. If you determine your available gambling fund monthly, you have clear idea on how much fund used for bets, then you will more likely be able to control your fund, risk and less likely lose all money for gambling.
Important steps must be taken when gambling, because carelessly managing finances can be devastating especially in gambling where it's easy to lose more.
Monthly needs must be met at least once and any remaining money can be used for gambling, but only a small percentage each month.
That's why it's so important to determine the amount of money you are going to gamble with. You set that aside and that becomes your budget regardless of your results. If you win something with it, great. You did better than many other players. If you lose all of it, you stop because you spent all of it. Under no circumstances do you add more money to that budget trying to recover or minimize your losses. That's when you end up performing even worse than expected.
Yes, for me, it's important to determine a budget for gambling, otherwise, my finances could be in disarray.
If I win gambling, I usually budget it again for the next month so I don't have to deduct from my monthly income.