Take a unit with more or less jump movement than ground movement. Good examples: Jenners, Uziel 8S, Gyrfalcon.
If a unit has JMPW1 (like the Jenner), under the previous edition you would declare a jump, look up what the TMM for that speed actually is, and then +1 for jumping. Now, you take the printed TMM (+3), +1 for jumping, and then JMPW1 tells you to reduce it by 1 for a final TMM of 3. It's the same number as before, but now you don't have to look up (or memorize) the alternate movement value's TMM.