That would be like defragging RAM - the situation is the same whether the data is transient or permanent. (That's why people - even manufacturers - call Android storage "memory". Ir's flash memory, used as permanent storage.) The pointer to storage has to change anyway, and changing it from block 1 to block 2, or block 1 to block 5 million, takes the same amount of time. Skewing a disk head all over the platter when a file is badly fragmented is time you'd notice without a stopwatch.