They’re unusual in legal documents, but I don’t object to columns in a long document like a contract or 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 (i.e., as if they were sitting on the same baseline). 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. The two most common options: set space between paragraphs to zero, or set it to be the same as the line spacing.