Addiction isn't only about getting karma for your character's dependence on a substance (or action). Don't forget, addictions can also get worse, or cause side-effects (like social penalties).
If your addiction gets worse because you are continually using, then you can burn-out pretty quickly. Some vices that aren't particularly dangerous of becoming addicted can be much more dangerous if you start out that way because the negative quality gives you a penalty on the resistance tests.