t: do a table of contents of an archive file.
v: view a file using the viewer in the mailcap(5).
x: extract an archive file.
This saves much hacking about with complicated command lines
as they embody all the decompression and decryption incantations
automatically.
In fact their knowledge comes from the mailcap(5) file,
extracted with the mailcap script.
You may also be interested in fixexts
which uses the file(1) command to correct the extensions on
mislabelled files
(which I find quite useful with netscape downloads because it
has a tendency to, say, decompress compressed downloads but
not rip off the .gz extension, etc).