The article linked in the first paragraph provides some good context: http://blog.imgtec.com/powervr/a-look-at-the-powervr-graphic...

Graphics developers need to know this stuff because certain operations can be very, very expensive on tile-based deferred renderers. Things like reading from the framebuffer, for example. On an immediate mode renderer, the GPU just has to queue up a DMA. On a tile-based deferred renderer, the previous commands have to be flushed first. And these differences are part of the motivation for new APIs like Metal and Vulkan.