Scala is an Expression-Based Language Not a Statement-Based One

I listened to a great podcast from the Java Posse Roundup 2013 on the train home last night: “Functional Programming”
During it, Dick Wall briefly described how Scala is an “expression-based” language as opposed to a “statement-based” one (because everything in it is an expression) and that this was one of the main reasons why he liked it. 
In short:

• if a language is expression-based, it means everything has a value (i.e. returns something),
• but if it is statement-based, some things need to rely on side-effects to work (e.g. in Java if/else doesn’t have a value, it returns something nothing)

Now, I’ve looked into the terms statement and expression before on this blog, but the full weight of the concept hadn’t then struck home.  Listening to the podcast was the final push I needed.  Consequently, I did a little more reading on the topic.  I was planning on writing a post here about what I found, but instead found Joel Spolsky had got there before me.