This makes it possible to make units heavier, which both push more & get pushed less by other units.
In particular, the diff does it for siege units & elephants.
This improves movement for these units in crowd situation, since they will now basically not move when other regular units push into them.
Contrast the videos below:
Before (NB: this is before rP26245)
{F2487851}
After:
{F2487852}