Why would you use Expression> rather than Func?

Question

I understand lambdas and the Func and Action delegates. But expressions stump me.

In what circumstances would you use an Expression

Answer 1

I don't see any answers yet that mention performance. Passing Func<>s into Where() or Count() is bad. Real bad. If you use a Func<> then it calls the IEnumerable LINQ stuff instead of IQueryable, which means that whole tables get pulled in and then filtered. Expression> is significantly faster, especially if you are querying a database that lives another server.