As a bike shop, we do a variety of different wheels - clinchers, tubeless, even the occasional tubular. Cycling tech has advanced far enough for us cyclists to sometimes get headaches over the different parts, types and even standards. Tubeless wheel setups are one of those advancements. And frankly, isn't necessarily the new kid on the block. Tubeless setups have been a thing for more than a decade now. And mountain bikers have taken to it so much that you might not even find mountain bike tubes in your local mountain bike store. They work great on mountain bikes. Some of the guys at the store ride mountain bikes and they run them tubeless. Hassle-free, no problems - everyone's happy.
However, in the road cycling world, tubeless setups haven't actually caught on. Perhaps it could be that pro cyclists don't run tubeless setups (they run tubulars, still, most times). Or could it be that maybe tubeless setups for road cycling isn't as effective as they are in the mountain biking world?
The difference between the mountain biking world and its uses and road cycling is stark. Mountain bike tires are high volume and run very low pressures between 15-35 psi while road tires run >70 psi most times. This high pressure is possibly the main reason why there's been a considerable number of tubeless setup failures where riders report sealant being pushed (sometimes in a fashionably violent manner) out of a puncture before managing to seal it.
In mountain biking, a pair of tubes may weigh more than a tubeless set up as the volume of the tube is high. In road biking, tubes are low volume and thus are pretty lightweight. There are even lightweight options produced by companies like Tubolito and Revoloop. In addition to that, riders can also opt for tubular tires.
This is definitely not to say that all tubeless setups are bound to be failures. Tubeless setups are what it's supposed to be - fuss free! And they're great until they are not. If you ride tubeless, you're likely to bring either a puncture kit or a spare tube on your rides. Puncture kits don't seal big punctures or tears like sidewall tears so you probably have to go use a tube. This is where things might get a bit messy. We've seen a couple of cases where the sealant has coagulated, making the tire difficult to remove and more often, making the valve difficult to remove. Now that will be a huge headache out on the roads where you're most likely not carrying any heavy duty tools.
However, all that said, we've seen people running tubeless setups perfectly. And they're honestly a joy to ride. We're just saying should you decide to run tubeless, there are risks involved in running it and you should know these risks before making that decision.