Being machmir is
a) an important way to grow closer to God
b) always safe
c) sometime appropriate, but often done out of ignorance
d) rarely appropriate and just turns people off to Judaism
e) something I never do
f) Leave this question out of my results
This question, again, leaves an important term undefined: "being machmir". Does saying "Baruch shem k'vod malchuto le'olam va'ed" after making the bracha "al mitzvat tefillin" count as "being machmir"? After all, we only do it (those of us who do) because we're afraid the bracha may be levatalah. How about putting on tefillin on Chol Hamo'ed? Or not putting them on? How about keeping your mouth shut rather than saying something that might - you're not sure - be lashon hara? Or getting someone to make Al Hamichyah for you if you're not sure you had a kezayis of mezonos? Or doing the yichud room jazz after the chuppah (after all, you don't need it according to some poskim)?
I assume that in this context, "being machmir" refers to adhering to chumras in situations where many current authorities would aver that doing so is not necessary. I can rule out (e). (A) may be true if it is qualified, but I do not think it is correct all the time for everyone: if competent halachic authorities (of course, who are they? But that would make this piece way too long) say that a certain action is permissible, then it's probably not true that it should nonetheless never be done by anyone. I don't think (b) is correct either, and for the same reason: there may be situations in which being machmir on a certain issue leads to an overall poor decision (like, for example, annoying one's hosts by refusing to eat their non-chalav-yisrael milk products). I wouldn't say it's rarely appropriate, though: most of the time, it seems to me, no harm results, and in such a situation, if you're interested, why not take kiyum hamitzvos seriously and play it safe? So (c) seems most correct to me: it's often not a bad idea, but I think that on many occasions, it is indeed done out of ignorance (isn't that what Rashi implies somewhere in his commentary on the Gemara when he says that the mark of a knowledgeable person is someone who will say "mutar"?).