I've working in welfare rights and also claimed benefits.
In general both legacy benefits and Universal Credit are structured so that you are always better off in work.
Low wages and part time work is "topped up" so that it's always better to be in some kind of employment rather than completely reliant on benefits.
In the past it used to be very common for single mothers to be forced to stay on Income Support for years at a time because childcare costs would swallow up their entire wages. Features like childcare elements, work allowances, tapers (where benefit income gradually reduces with income rather than abruptly ending) are intended to prevent this kind of "benefits trap".
"Better off in work" means better off for your specific circumstances. So its often possible to point to someone who seems to be doing "better" on benefits. But it usually turns out that they have different circumstances (higher rent, disabled child, etc).
I've even seen posters on here complain that someone is getting "more than my wages in benefits" and it turns out OP is married to a relatively high earner and is comparing herself to a single parent. That's obviously not a like for like comparison!
Having said all that.......
Any benefit system will have a somewhat arbitrary cut off point for entitlement. If you're just under or just over that point (which will be different depending on your circumstances) then you have some tough choices to make about whether you should work and if so, how many hours.
I'd always recommend people do a "better off calculation" before starting a new job. You can ask for this at a CAB or just mess about with Entitledto.
Try entering different figures for earnings, working hours and child care to see how it works out. Don't forget to factor in the cost of getting to work.
Sometimes you can be technically better off working more, but the difference is swallowed up by work related expenses. Or is simply too small of a difference to feel worth it to you.
I can certainly relate the the poster up thread who refered to a "sweet spot" of part time work topped up with benefits.
When I returned to work after mat leave my "sweet spot" was 25 hours per week. Once Tax Credits and childcare costs were factored into the equation the difference in income between 25 and 40 hours wasn't worth it to me.
Ironically I also cost the state much less at 25 hours as a large proportion of my Tax Credit entitlement was the Childcare Element.
Now DS has his autism diagnosis my sweet spot is 9 hours. This is enough to make my benefit income more livable but not not enough to upset my entitlement to Carers Allowance.
I'm now in the position where someone else could easily point to me and say "Dashoflime only works one shift and she gets more in benefits than I get in wages" and, depending on their circumstances, this might be true.
However, if I returned to my old job, DS would still have his DLA and I would still have my Disabled Child Element in my Tax Credits. So overall, I would be "better off" working more, as the system intends.