I think it also matters how you see the drug in question. Weed isn't alcohol, and its effects and side-effects aren't really comparable. Some people smoke so often they don't see being high as an altered state (and this does not mean they are addicted or abusing the drug, either). Me, I smoke quite a lot, and if I didn't read while high I would never read. But I also go to work "high" and I do everything normally. Why I smoke is a different kettle of fish (having to do with social anxiety), but I can be high and you would never know it. Heck, I've even lifted weights high.
Not every high is the same, either. There are stoners who are sh*tfaced lumps most of the time, and they smoke in order to get to that state. Others have a quick puff and carry on with their days. Some types get you up and alert while others are heavier and make you slow.
Like others have said, all personal preference.