It`s situational, if you`re out of targets for a while, as is so common these days, and you`re base is just 1-4 planets, and you CAN sit in NP and research, go for it, drop and research till the large is populated, it can`t hurt anything. But if there are a ton of people around for you to hit, just plunder it now, and take the gamble that perhaps something you get from one of the other targets will make your fighting worthwhile.
That`s just my opinion, of course.