Depends on the site but the general rule is this: The easier it is to acquire user information, the better. If you can get a new registrant by the simple act of "clicking", you will grow faster. Asset values are grown by registered users which translate = $$$.
New registrant = Take 5 minutes and fill out form, confirm email, blah blah (10 minutes.)
New registrant = Take 3 seconds. Click. Done.