Equivalent to print FILEHANDLE sprintf(FORMAT, LIST), except that $\ (the output record separator) is not appended. The FORMAT and the LIST are actually parsed as a single list. The first argument of the list will be interpreted as the printf format. This means that printf(@_) will use $_[0] as the format. See sprintf for an explanation of the format argument. If use locale (including use locale ':not_characters') is in effect and POSIX::setlocale() has been called, the character used for the decimal separator in formatted floating-point numbers is affected by the LC_NUMERIC locale setting. See perllocale and POSIX.
For historical reasons, if you omit the list, $_ is used as the format; to use FILEHANDLE without a list, you must use a real filehandle like FH, not an indirect one like $fh. However, this will rarely do what you want; if $_ contains formatting codes, they will be replaced with the empty string and a warning will be emitted if warnings are enabled. Just use print if you want to print the contents of $_.
Don't fall into the trap of using a printf when a simple print would do. The print is more efficient and less error prone.