Control the amount of money in the portfolio.
For long-only portfolios the amount of money allowed is controlled by the gross.value argument. This ultimately specifies a range of allowable values, but may be given a single number.
For long-short portfolios the possible arguments are gross.value, net.value, long.value and short.value. Each of these really specifies a range of allowable values, even if given a single number.
See also Turnover Constraint.