Zhuyin (bopomofo) vs Pinyin I have learnt to use both zhuyin and pinyin for spelling out the pronunciation of a character. As far as I know, the two systems serve the same purpose and are interchangeable in terms of syllables. 

As such, why would there be two standards? Does each have a specific context/setting in which they are used? Which one is more popular in general?

Thanks in advance!
Zhuyin is commonly encountered in Taiwan and Taiwan-centric overseas communities.  Not sure about its prevalence in other overseas communities a la Singapore, but I've found zhuyin easier to use with vertical text Chinese as is printed commonly in Taiwan and elsewhere, and suspect Zhuyin/bopomofo/bpmf would be more popular in those regions due to the better compatibility with vertical text.  If you want to use the many excellent classical chinese training materials printed in Taiwan you'll need to be able to read bpmf.

I also suspect you'd find that typing bpmf is slightly faster than Pinyin because it uses single symbols for sounds like "eng" that require multiple keystrokes in the Pinyin case. And I personally find Zhuyin aesthetically less disruptive ;)