Many users of the original Nexus 7 remember how slow the device could get after a few months of heavy use. At least part of this problem has to do with the way NAND flash stores and deletes data. Android 4.3 comes with a little-hyped feature that could be huge for performance in the future – TRIM support via fstrim.

2013-07-29 20_33_28-b87937cdea689594a293979b30b13054e7455dee - platform_system_vold - Git at Google

There were ways to run the fstrim command on devices before, but it required root.