You are using gulp-plumber to report errors in .less files. But it stops gulp on error and user has to rerun it every time.
I use the following function to report errors:
function handleError(err) {
console.log(err.toString());
this.emit('end');
}
and then:
.pipe($.less().on('error', handleError))
So it has the same output on errors as gulp-plumber, but doesn't stop gulp.