Cutout vs Cutout Mipped?

What is the difference between the CUTOUT and CUTOUT_MIPPED block transparency option, and which should I use as my default? Which is more beneficial for performance?

I understand what mipmapping is, but will it make any noticeable difference unless there is a enormous field of the block? Especially when it is used for plants, because even if placed in a large square, the spacing is is not completely consistent because of the plant x/z offset.