You can do pretty much anything, some examples:
1) if the user typed in the word "support" or "help" you could change the recipient to email@example.com, but if it found "business enquiry" forward it to firstname.lastname@example.org.
2) Same goes for a City field, if the user is in London you could send the email to the London branch.
3) Or if the form was submitted on a weekend, when the offices are closed, you can send a confirmation email like "Thanks for your email, unfortunately we are out of the office, will get back to you on Monday".
4) If there is a budget field and the user types in "1,000" then forward it to email@example.com, but if the user types in "10,000,000" then the boss will probably want to deal with that juicy client himself.
There's plenty of examples really, the idea is to have fewer forms on the site (or even just one) which then through some smart coding can do custom actions or change certain things.