"He lives just round the corner from her" is often taken to mean "He lives very near her". He may live several streets away. It may be necessary to turn several corners to get from his place to hers. This is the
figurative meaning of the phrase.
If it really requires no more than turning one corner to get from one place to the other, the speaker may wish to cancel the figurative meaning of the idiom. To do that the speaker uses the word "literally", meaning "exactly what the words say". The speaker wishes us to understand the distance in terms of the
literal meaning of the phrase.