The thing is with being on a low wage or on benefits (or a combination) is that you have, in general, no safety net. So any kind of unexpected expense (broken window, DCs losing or destroying items of school clothing, illness that means you can't work and lose some pay, illness of family member that means extra expense on fares to and from hospital etc) tends to mean you end up borrowing money. And if you are poor, you'll end up borrowing money from somewhere that charges high interest rates - if not an actual loan shark then certainly a sub-prime lender. And so that debt will accumulate and linger, and there will be another bite out of your weekly budget. So if you're managing on less than you're 'officially' getting, because a chunk of it is going to pay off a debt, or even if you're just screwed right down to the margin anyway because this is the month the gas/electricity/water all needed paying at once, and then one of your sources of income is a couple of days late, or even one day late, so all your standing orders and direct debits bounce and the bank immediately charges you about £100, then yes, well, you might have a day or two where you might have to give the DCs bread and marge and not eat at all yourself.
ANd don't ever think this sort of shit couldn't happen to you, because it could. Very easily. All it would take would be a wave of redundancies in your industry, an illness or accident that stops you working (either because you're disabled or a family member is in need of constant care), some trend or technological advance making your whole line of work obsolete when you're a bit too old to get another job on anything like the pay you were on...