Importance of learning 180 rotate

[vipjun]

i think the gain is about 5% - 10% speed at the most.  only 3 pieces out of 7 are going to need that rotation.
BUt it's good for games like cultris where 180 spins can help balance your field.  In games like nullpo 180 spins are used less because of the 6previews, since stacking without softdroping for twists is usually preferred.

some napkin math used in the calculations

There are  1,3,3,4,4,4,3 22 rotation states of which only 3 have a 180 rotated state that are distinct.

that is 13.6% ~half the moves you will be double tapping or das tap so about 7% of your placements will benefit from 1 less keypress which is somewhere between 4 - 10 frames per keypress.

Another example is,
In 40L somewhere between 70-90 rotations are used , so about 5 - 7 180 placements per run.  Only half of those will save you time so we're talking 3-4 keypresses   ~.5 seconds shaved.

this is way less beneficial than going from 1 to 2 rotations where 6 of the pieces are effected.  

[Paul676]

far less than 0.5s. more like 0.2 max. Not that this isn't a good reason. For all but the best players it is something good, but if you're not sub 25 there are other things to learn. 4 ain't a 1