Originally Posted by Dave Mayer

Let's break this down once again (sigh):

Fat tires: They are heavy and require fat heavy rims. Good for comfort I guess. They feature high wind resistance and high rolling resistance. Yes, if you pumped a 32mm Conti GP5000 to 100psi, you may save 2 watts of rolling resistance over a 23mm tire. But you pump the 32mm tire to 70psi, and then the rolling resistance for the fatter tire is now more. Besides, tire rolling resistance is a distant second-order drain of watts.

Sloping top tubes: easier to get an off of the bike if you have hip problems. More standover height is good if you are riding your road race bike over a minefield of rocks and roots, and your 'tender parts' come in frequent contact with the top tube. Guess a good thing on a road race bike. BTW, due to the extra frame reinforcement required in the seatpost cluster, and the longer seatpost, the sloping top tube design is actually heavier than the traditional road bike frame with a horizontal top tube.

Tubeless: If you are flatting out every week, good I guess.

Discs: good if you are riding down a steep mountain road in the sleet carrying camping gear with frozen hands. Otherwise, heavy, fussy, expensive and unnecessary.