i run tubeless on my mtb...the point is that they don't flat (easily), the sealant prevents it. been using for over 2 years of some pretty aggressive singletrack & only failed once, while i cannot count the number of flats i had in the previous similar time frame.

it is entirely possible to set up a tubeless system on just about any wheels, even without rims & tires that are specially built for it. in fact, stan's does make a "tubeless conversion kit" that i have seriously considered for my "road" bike.

the biggest downside (beside xtra weight & it's not cheap) that i can see is that tubeless does make it a real hassle to change tires & since i like to switch the tires on my fg bike pretty often, i passed on converting it to tubeless.