Well, the JLPT is actually very often by employers in Japan to gauge a foreigner's Japanese language skills. There are many practical reasons for taking the JLPT rather than to just test yourself.
you can take whatever level you want without passing for the others, im going to take 3 level this year, i made 4 level the past year, it was easy but i think the 3 level test will be more dificult x.x.. however.. i hope to pass xD..