Tire Selection and Tubeless Wheelsets:
Tires are the most important part of your bike. Tires win races and tires lose races.  You can squabble over hard-tail vs suspension, or gearing and geometry for what makes a better bike for you.  It is important to know all these factors , and many others are swamped out by Tire Selection. Your tires make your bike better, or they can make your bike worse. 

Tubeless is one of the best options for your bike.  Many of the newly sold MTB's are running tubeless tires.  If you do choose to go tubeless, you must use tubeless specific rims with tubeless tires. You can get non-tubeless specific rims to seal, and hold air, but that will not last forever. A tubeless rim has a special hook design that matches the new tire designs to keep the tire from burping or worse. A tire could come off the rim completely. On a fast downhill, that is big trouble.

Since the introduction of tubeless, Pinch Flats have almost been illuminated.  (AKA: Snake-Bites because of the double holes they leave in the tube) Pinch flats often come from low tire pressure and overly aggressive trail riding.  After thorns, pinch flats were the second most common type of tube flat.

CX / Gravel Bikes: Tubeless is a huge benefit for CX bikes. Still, not many folks use them.  With the very thin CX tire castings, tread patterns, and super lite weight, these tires are very prone to thorns and snake-bites equally.  Your CX bike would really benefit from a Tubeless conversion.  Almost 2 pounds of weight loss shedding the tubes, and you can run lower tire pressure for a softer ride and better traction.    CX tires gain a lot of traction in the 30 - 40 pound inflation range.

Note: On my long 40+ mile CX rides with tube tires, almost 1 tube change per ride. Since going CX tubeless stopping for tire issues is almost eliminated. 

Not everything is perfect: One main downside of tubeless tires is Sidewall Slicing. Sidewalls on mountain bikes are soft and flexible. This is a design feature for better traction.  As trail riding dynamics apply force to the tire during a bounce or jump, the tire will bulge under compression.  As this happens the sidewalls of the tires expand outwards beyond the width of the tire tread.  If a rock surface or other object is properly placed, it could slice through your tire's sidewall.  CX tire sidewalls slice just as nice.

Experienced tubeless riders know this happens more than once.  These incidents take a great tire and makes it junk in seconds, while ending your ride. Sidewall slices can not be repaired.  For this reason, always carry a spare tube with any tubeless wheelset. It is messy putting a tube in, but it will get you going again.

This was not an issue on Tubed Tires. With a tube in the tire, the sidewall is not nearly as flexible, and tire pressures run higher to avoid pinch flats. Also when tube tires were popular, the tire manufactures did not put a lot of focus on the weight of their tires. So a lot of tires had thick sidewall castings. Slight sidewall tears were also compensated for with the tube.  You would never know a slice occurred unless it was severe enough to penetrate the tube, which was a very rare occurrence... if ever. Many tire manufactures are all working on these sidewall issues, all trying to make sidewalls better as tubeless tires mature.

Sealant: Tubeless tires are also self sealing for small puncture holes. Could be from thorns or glass or sharp rocks.  About 3 oz of fluid sealant is resting inside the tire waiting for any exposure to fresh air.  As the puncture lets air out of the tire, a small amount of sealant fills the hole and quickly seals it.  This is great for MTB's that run low tire pressure.  On CX tires, you are running between 40 and 60 pounds of pressure.  Sealant has a much harder time keeping the hole sealed at these pressures. It gets pushed out, even after it has sealed for an hour.  

Tubeless Repair Kit: Recently a few manufactures have come up with a way to plug your tire while on the trails.  These plugs simply push into the tire, and when you pull the tool out, a rubber plug remains in the tire's hole. Then simply cut away the extra plug sticking out to make it flush with the rest of the tire, and you are good to go with a permanent tire repair.  (See below for these tools)

Casting is the method a manufacture uses to form a tire.  Because of sidewall slicing, it is highly recommended you get Thicker Casting Tires for the Rear. Front tires do not get sidewall slices nearly as often as the rear.  Mostly because at faster speeds your riding weight is shifted back over the rear wheel.   Shifting your weight back also helps your steering control at faster speeds. Fast speeds and tire bulge on transients means more odds of sidewall rock contact. 

Most tubeless tire manufactures offer their tires in both thick and thin castings.  The Thinner Castings saves weight. You are only talking a few hundred grams, but rotational weight has a multiplier effect. So the weight difference can be noticed.  Thinner castings also have a bit more traction in off-angle turns.  The sidewall flex helps the tire conform to the trail.  These statements are not ghosts.  There is an immediate and noticeable difference in tire castings.  Thicker castings are more slice resistant. Stiffer riding, and the sidewalls are not as flexible.