A little habit:
If you were to haunt me, every so often you would see me open up a
new terminal window, run
cat >/dev/null', and paste or type something there.
What I am doing with this peculiar behavior is simple: I'm arranging for a slightly more persistent text storage than my X selection. I park any number of things depending on what I'm doing; snippets of text from fishing back in editor undo, commands that I'm temporarily re-running, and so on.
There's nothing particularly special about
cat in a terminal window
for this. There's any number of other programs and ways that I could do
this; it's just that this way is the fastest and most convenient in my
environment. Your environment is probably different, especially if you
keep an editor going all of the time (if I always had Emacs running, I'd
probably just paste things into a scratch Emacs buffer).
xclipboard should be ideal for this. In practice it
sadly doesn't work out, partly because its version of cut & paste is
significantly worse than that of terminal programs.)
Note that in some ways using a terminal window is a bad idea. I always have to make sure that any tabs are unimportant, because they're probably going to turn into spaces by the time I paste the text back into its eventual destination.
(I would really like an X terminal program that was smart enough to preserve tabs, but I haven't run into one yet.)