This is useful if you are performing the same operation on a number of similar files. Often, people combine many different methods of packing, such as taring a group of files, compressing the tar file, and then uuencoding the compressed tar file. To 'undo' these operations, you need to perform the reverse operations in the opposite order in which you executed them. In the above example then, you would 'uudecode' the file, 'uncompress' the resulting file, and finally 'tar -xvf' the result. Not compression, just grouping.
Converts file to a form which uses less space.
Expands file back to original form so you can read it. Converts file to a form which uses much less space. Expands file back to original form so you can read it. Converts file to a form which may be mailed or posted. Converts file back to binary form so after you download it to a computer, you can read it.