The answer is obvious. If you took too much to throw up then you are taking more tolerance to amount taken ratio at every single heroin session constantly changing keep in mind, than you did when you didn't throw up. For me, at least, throwing up is a sign of a very high dose. So if you don't throw up, well, you're not taking a high enough dose to get you into the vomiting range. To relate, it's like taking too much speed and procurring more negative effects with very little positive effects, eventually the negatives outweigh the positives. I usually prefer to not take so much dope that I puke my guts out.
One more thing, throwing up seemed to be a thing I did when I was beginning using heroin and was adjusting to dosage levels. Like itching, the puking eventually subsides.