Show all variables affecting this Test
It shows you the number and values of all (presumably ;)) variables influencing this test page.
Technically it goes all the way up from the test page URL analyzing pages through ?edit command.
If some variable is found several times you see those several definitions. Depending on circumstances it can be a problem or just a regular situation.
In any way it shows you what Fitnesse doesn't - all variables in a single place!