At its heart, Wufoo is a form builder. If you need any type of form, you can build it super quickly by selecting and customizing the fields you need in Wufoo's fantastically easy to use form builder. I can hardly imagine a more useful web app for web designers and developers.
But what is a form, at its essence? Just a means to collect data. The important part is what you do with that data. You can do all the obvious stuff. You can have entries emailed to you. You can build reports from the data. You can explore the data inside Wufoo, or use the API to access the data outside of Wufoo.
Those things are just the tip of the iceberg of what you can do with data you collect with your Wufoo forms. There are built-in integrations! For example, say you have a form that includes an email address field, and you'd like to ship that email address over to MailChimp or Campaign Monitor into a particular mailing list. That's just a few clicks away. Or say the form has some element of lead generation and you want to send the details to Salesforce. Or you want to tweet data from the form upon submission. Same deal, just a few clicks.
One of my favorites is that Wufoo works tremendously well with Zapier. That's the whole point of Zapier, you can use it to connect services together! For example, the Ask a Question form over on the ShopTalk website not only emails Dave and I but adds the question to a Trello board for us to organize into shows. We could easily have it integrate into Evernote, dump into Google Sheets, or work with any of hundreds of other services. Wufoo is such a great source of data for integrations, it begs for playing with.