K.P. makes a great point. IPA isn't as clear-cut as is often assumed, especially when it comes to vowels.
To be honest, I've never understood how linguists decide at what point a slight change in lip/jaw/tongue position consitutes a separate phoneme. /ɪ/ and /ə/ are so close together in English that they're virtually indistinguishable in some dialects of English. On the other hand, the English word "pool" and the French word "poule" both contain a /u/ vowel, yet the two words sound very different.
Moreover, IPA as it's used for language learning is based on British RP pronunciation, which flattens the variety caused by different native accents - a phonologist would transcribe "pool" as /pʉ:l/ in Australian English, but for language learning purposes it's still written as /pu:l/.
Anyway, the important point is that you shouldn't assume that just because a phonemic symbol exists both in your native language and target language it means the actual sounds are identical, schwa being a notable example of this.
Michael, KP, Sudeep, and Alan...
Thank you all for contributing to this discussion. All your comments were quite informative.
Thank you very much, Richard for bringing this topic. I didn't know much about this topic but you made it simple and clear with definition and examples.
I think the English learners should have the basic knowledge about this so that they can make a clear distinction while writing and speaking, at least, it will be easier to pronounce some words correctly. For example, if someone is not aware of this, then he may pronounce "about" as it is or as "Ebout" with stress in the first syllable. So, by having a bit knowledge about this subject, one can avoid such small mistake related to pronunciation.