One common sentiment I've seen is that financial planning often only makes sense if you have a net positive income anyway.
Crude hypothetical;
You are stuck working minimum wage jobs on zero hour contracts for whatever reason. Your rent and food costs eat the majority of your monthly income. You have to drive for work but can't afford the up front costs for a good car and public transport is not reliable, so you are paying over the odds for fuel, repairs and frequent replacement vehicles (more old clunkers because that's all you can ever scrape together the money for). The remaining money sometimes covers your bills and other costs, but sometimes not. You have had to resort to emergency or payday loans to cover shortfalls on several occasions and this has left you with considerable debts. Most months now you are deferring/skipping payments, occasionally taking on more debt or missing a bill payment to keep the situation from escalating further.
Now you come into some money. A bonus, a gift, some windfall. It's enough to pay your monthly bills with a fair amount left over. What is your best option?
Well, the money itself isn't enough to clear your debts and won't change your monthly position as far as payments go. At most it will cover them for a few months before you are back in the exact same position as you were before, without even giving yourself much in the way of breathing room.
Alternatively you could buy things that give a direct improvement to your quality of living. A new TV, games console, whatever. OK, so you are back on the monthly grind immediately, but at least now you are on the grind with something to distract you from it.
I've heard a number of stories where people who have tried to save money from a position of poverty simply see it evaporate before they can use it. Money doesn't multiply for poor people the way it does for those with assets and the ability to invest. Trying to hold onto it is trying to hold onto vapour. Not spending it means it will just go away without doing anything positive for you. Better to convert it into things with obvious benefit.