There is no big difference between those functions except the syntax:
$(\'.target\').append(\'text\');
$(\'text\').appendTo(\'.target\');
A
It's useful for when you chain a few jQuery actions together. like so:
$('.target').css({display:"block"}).fadeOut().appendTo('.somewhere');
// appends target to somewhere
or:
$('.target').css({display:"block"}).fadeOut().append('.somewhere');
// appends somewhere to target
those two are different actions, hence it is useful to have them both.