Spring Expression Language (SpEL)

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The Spring Expression Language (SpEL for short) is a powerful expression language that supports querying and manipulating an object graph at runtime. The language syntax is similar to Unified EL but offers additional features, most notably method invocation and basic string templating functionality.
I read through the entire SpEL chapter but I still fail to see the practical usage of this technology. Would anyone able to elaborate it with an example? Why would we want to build a object graph in runtime?