\balance that activates the equalizing of columns of text on
one page. Since this sometimes causes problems with floats and footnotes, it
is better to issue it only on the last page. More precisely, it should appear
somewhere in the text of the (unbalanced) left-hand column of the last page.
Obviously, it only makes sense for preprints; in other modes, it has no
effect, and may safely be left in the text.
The counter command \nobalance undoes the equalizing if this should be
necessary.