The general rule-of-thumb: the shorter your Contact Form, the more apt visitors are to fill it out and sign up.
Whether your form is minimal or asks for more detailed information, though, depends on your goal.
If your goal is to get as many email addresses as possible because you need thousands of folks on your email list, only ask for their email address. Maybe a name. The more info you ask for, the less likely they’ll fill it all in. (You can ask for the rest later, after they’ve taken the initial step.)
This is true for those who are selling products. The more email addresses you have, the law of averages equals out to more sales.
But if your goal is to get qualified leads, you’re better off requiring them to be more detailed up front.
Why? Because you’re not after just anyone, you’re after the prospects who are most likely to do business with you. This is important for those offering a service, for example, copywriting or consulting.
As Chris Marlow points out in a blog post addressing this, when you capture a prospect’s website, you can visit that site to learn about her company before contacting her. That can help in learning whether she might be a good fit as a client. You can read Chris’s entire post here.
If someone refuses to give you more than a name and email address, chances are she isn’t seriously looking for your services anyway. If your visitor is serious, she’s not going to be deterred by being asked to give you a little more information.