i read the other night that some strains don't really like it - but, what it will do is cause the plant to shoot off multiple big colas where there would have been just one.. some people top several times and end up with a bushier plant i imagine..
so, i would say it is a good thing unless you don't have the space for the plant to bush out or you know that the strain you're growing is one that does not tolerate topping..