https://www.khronos.org/registry/gles/extensions/EXT/EXT_copy_image.txt

The use of this extension can potentially make texture to texture copies faster. These copies are done today by binding either the source or target to an FBO and then calling glCopyTexImage2D or drawing the source texture onto the destination. This takes an unnecessary amount of CPU time on the critical main thread in the GPU process.

Many Chromebook devices (Haswell, Broadwell, Skylake today) use texture to texture copy operations for to initialize contents so making this faster will have a significant impact on ChromeOS.