If you spend much time in binary groups, you may grow tired of hitting X u, n, RET all the time. M-x gnus-binary-mode is a minor mode for summary buffers that makes all ordinary Gnus article selection functions uudecode series of articles and display the result instead of just displaying the articles the normal way.
The only way, in fact, to see the actual articles is the g
command, when you have turned on this mode
(gnus-binary-show-article).
gnus-binary-mode-hook is called in binary minor mode buffers.