The external SD cards for Samsung devices can only hold data type files, ie. Photos, Videos, documents, etc. All apps have to be saved to the internal memory. Only the app's data files can be moved to the SD card. So, yes, having a larger internal memory will expand the functional life of the tablet before it runs out of room for your apps. Also, the 128gb tablet only has 6gb of RAM, whereas the 256gb tablet has 8gb of RAM which increases multitasking ability and general processing speed.