see, with weed i would say do some exercise to sweat it out the system or mix it with booze to get blasted...
i admit i dont know much about heroin, but if you have to use a lot to get a decent dunt then well you dont want to become dependant on it.. taking a break will prevent you from getting sucked into it and eventually facing horrible withdrawl. oh and of corse when you return you'll get more of a bang for you buck..
basically, i think me smokin weed consistently caused enuff problems.. i used to get really good dunts if it was my first smoke of the day or time of day (eg. after dinner it would be upto 3hrs since my last smoke) and well that caused enough problems. i very rarely gave it any sort of day break, and if i did id appreciate it sooo much more.
i hate to state the obvious, but i dont think you should be fucking with heroin regularly. no1 wants to become an addict but if you ignore this 'threshold' then you could be drawn closer towards this possibility.
of corse, i dont know how frequently your using, how your doing so, and how much is in one of yours bags...
yes i know its not an answer to your question.. but, um.. just cause for concern
let drugs change the way you think, but dont let them enforce you with a one-track mind!