If you're guaranteed money, you do away with the marginal effects of means-tested benefits. Basically, if you're a low income earner it can happen that you face a very high effective tax rate, in many countries. If you're guaranteed money, you don't have this marginal tax problem; you can sit on your ass or work for a bit of extra money. If you already make more, take it as a tax allowance.
This in turn means you do away with the means testing system. No more forms to fill out; no more mandatory courses that do nothing but line the pockets of the course provider. No more looking over people's shoulders to see if they're cheating. No more pressure on doctors to write iffy diagnoses.
There are of course issues with this system. For instance what do you do about immigration?