I can understand the general principle that being in work should be better-rewarded than not being -- but then again maybe there will come a point where that's simply unsustainable as an attitude -- but wouldn't it largely be better achieved by improving the lot of those in work*, rather than "punishing" those out of work? It depends on the circumstances of the person in question.
And besides, the benefits cap also hits those in work, but receiving eg Housing Benefits in particular, so the idea that the cap only affects "work shy layabouts" is grossly unfair.
*Yes, I appreciate that the current government has pushed through planned rises to the minimum wage (now Living wage; somewhat odd from a party that barely a decade ago was opposed utterly to the principle, but welcome all the same). Wages have generally stagnated in the last few years overall, though -- and that's not just down to the 2007 crash either, as they were starting to rise again in 2015/16.