They only really give you enough for food on UC (actually, not even that - after rent, I'm expected to live on £7 per day right now on the basic level of income), which means you never have enough to replace anything vital.
Right now I need new footwear for exercise (IE trainers) but just can't afford it, so sooner or later I'm likely to injure myself. Again. I already sprained my ankle recently (because of my old, falling-apart trainers) but my health conditions are such that I need to exercise regularly or I will suffer more.
Furthermore I also need a wifi dongle. My old one is fucked. If it dies entirely, I'll not be able to replace it any time soon because I don't want another dongle; they die within six months, it's not cost effective. So I'll need a wifi hub. These cost 20-30 quid. I can't afford 20-30 quid because I need it for food.
I actually recently moved because in my old place, if anything broke down, we had to buy a new that thing collectively. I just knew I couldn't afford to contribute. So I've moved into furnished accomodation instead so that if anything major breaks, I don't have to pay. But this means higher rent and less to live on week to week.
My entire life for the last five years or so - since the benefits freeze really started to bite - has been being constantly anxious about things breaking that I can't afford to replace without begging for money from friends or relatives.
That has obviously really, really helped my PTSD recovery.