They’re unusual in legal documents, but I don’t object to columns in a long document like a contract or a settlement agreement. Columns are an easy way to get a shorter and more legible line length without having to use large margins. On a standard 8.5″× 11″ page, two or three columns are fine; four is too many.
Usually columns look neatest when the rows of text are aligned vertically between columns. Look at a decent newspaper for an example. Getting this result takes a little extra effort. Note your line spacing and make sure any space between paragraphs works out to a whole multiple of the line spacing.