What are the disadvantages with sending the rest of the form to the user’s email?

We decided to change how our sign-up form works. Instead of filling out the whole form and then sending a confirmation email to the user to activate their account, we only ask for their email on the sign-up page, and the rest of the form will be sent in the email.

We made this change for these reasons:

• If you mistype your email address, you won't risk sending all of your personal information to someone else's email.

• People won't be able to send confirmation emails that "trick" other people into activating their account with your email address.

• Our form is pretty long. In the original system, users may get intimidated by the number of fields they need to fill out. In our new system, they'll be more likely to fill out the rest of form, because they've already registered their email address (they've already started the registration process, so they're more likely to finish it).

There're many advantages to this system (or so we thought). What are some disadvantages of this system?