If three files os size is like [1000, 30, 2]
To access the file having size 2 in a "tape" which read sequentially like our old audio cassette we need to read "unnecessarily" 1000 and 30 file sized also.
But if arrangement would be [2,30,1000] to read 2 bytes we just access it, no need to wait to skip over 1030 bytes to reach the required file.