The main difference of posits (the variable sized exponent) is slightly worse for hardware (but not much). Posits, however win back a lot of points because they

The main difference of posits (the variable sized exponent) is slightly worse for hardware (but not much). Posits, however win back a lot of points because they remove a lot of special cases. FP hardware generally needs special checks for NaNs, Infs, -0 and subnormals. Posits only have 2 "special" numbers 0 and NaR. The problem with subnormal floats isn't that they are inherently slow, it's that they are different and rare which means they aren't well optimized for. With Posits, everything is the same, which reduces the number of branches in hardware.