Not only knowledge of vocabulary and idiomatic expressions is important for language fluency. Being able to work with possible metaphoric meanings of what is written or said is just as important, maybe even more. It helps covering the gaps where knowledge runs short.
A lot is said about how knowledge of vocabulary and idiomatic expressions is important for text interpretation and understanding language in general. Lots of words are also spent on the importance of learning in context.
There is little doubt that a rich knowledge of vocabulary and idioms is an important factor in understanding and producing language. However, there are always moments where this knowledge is not enough. The first thing that comes up in most peoples minds is, look words up or ask someone for the meaning. But, what if this isn't possible?
Actually, situations in which it is not possible to look up or ask for the meanings of words are more common than those in which it is possible. Moreover, even when it is possible, the process is often to difficult and to slow. These are situations where thinking in metaphors is useful. When words don't seem to make any sense in the context at hand, trying to find a metaphoric meaning very often shows you the meaning of those words in that context and it is even likely to be one of the meanings that can be found in a dictionary. This makes thinking in metaphors to understand words and texts at least as important as knowing many words and idioms. It is a fast and flexible way for understanding what others want to say.
That's not all. Apart from making the process understanding of what is heard and read more time efficient, it results in pretty much unconsciously and automatically improving ones knowledge of vocabulary and idioms. It is learning in context by nature.
When I explain this to my pupils they just start trying to find metaphoric meanings for expressions that don't make sense to them. After that it is basically a matter of, the more they do it, the better they get at it.