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I don't know actually, it's a good question.
Thinking about it, there are riders who rode on tubeless during the Tour Divide (in the past, it was slime inner tube which Jill Homer have positive experiences with) and it work for them, you still carry a spare inner tube anyway if all the sealant gone from it.
It's very very useful for MTB because of the increase risk of getting punctured, however on road, I honestly don't know, it's not necessary IMHO, I'm not the person to ask because I honestly can't see myself using it in the future, especially when tube/tyres worked perfectly well for me.
Also for those who run touring tyres on their tourer, like a Marathon Plus which is pretty indestructible already, I can't see a reason why you should go for it unless you want to reduced a tiny amount of weight (and increase comfort slightly).
(I don't run tubeless on my NFE, just lightweight butyl inner tube and tyres).
Don't worry too much about it, unless you're morbidly overweight riding on tiny tyres.
28mm at 75psi will be fine for instance (ran that for a year, definitely don't need more than that on the rear), so the bigger you go, the lower.
With Crest, 28mm is the absolute minimum for road riding.