[CRConrad]

> Do you need an address to contact people on? You'll must make sure that the user can read the emails sent to that by you. Do you merely use it as a login-handle?

Pretty humongous dick move to use someone else's email address as one's own login for some website, wouldn't you agree? What if it's a popular website, and the owner of the address would like to use it for their id; why should anyone else be able to deprive them of that?

And thus it's also a dick move from the site operator to allow those dicks to do that. So no, it doesn't depend: Just don't accept untested email addresses for anything.

[berkes]

Again: this depends on the business case.

Not all web-applications with a login are open for registration. Not all are public. Not all are "landgrab". Not all have thousands of users or hundreds of registrations a week. Not all are web applications and not all require email validation.

Some do. But, like your niche example proves: the business-case and constraints matter. There's no one size fits all.