if you need append some string to element and need set some attribute on these string at the same time,you'b better use appendTo funtion.because you can use this function like this:
$(str).appendTo('.content tbody').data(action, EditAction.Add);
but is you use append function,you should use it like this:
$('.content tbody').append(str)
$(str).data(action, EditAction.Add);//it can't work some times
as comment say,it can't work some times,especially in the IE.
the another difference is you can use function to append something,the syntax is append(fn).