I'm not sure why you'd think it is only one thing, OP. There are various kinds of benefits and various reasons for them.
Almost everyone thinks it's a good idea to have a safety net and support people who really can't work, or can only work at jobs that have very low productivity. By which I mean jobs like my local cafe where more than half the employees have intellectual disabilities and need a little more support in their work than would be usual. Their wages are subsidised in part by the government. This benefits them, but also the community.
But if there are people working standard jobs, they shouldn't really need benefits to top them up. Those kinds of benefits, aside from being a subsidy for business as others have mentioned, tend to create a lot of unintended and unhelpful incentives, and even unfairness, in the wider system.
Of course there are also people who become leeches on the state.
I think a real issue is that what can often happen is that people stop thinking of benefits as something provided by other citizens, through their work, to help those who need it. And instead they think of it as the duty of the state - an abstract entity - to provide for them.
And its a bit like Walmart vs the local business where the owner is a local figure, people might not dream of taking advantage of Bill who they know and see how hard he works, but they are happy to get one over on Walmart. This is why people don't think it's in any way dodgy to reduce work hours to reduce income and keep a benefit, they just think it's sensible. They don't think about the fact that someone else, a person like themselves, is working to provide that money.