Protect your list quality with double opt-in
Picture this: you spend good money on a concert ticket but when you arrive at the venue, the security crew isn't checking anyone's ticket. They're just letting anybody walk through the entrance without validating that they actually bought a ticket or are authorized to be there. This could lead to a big crowd that is totally out of hand, who aren't even interested in watching the headliner. This degrades the experience for everyone involved.
Your email list is no different. In fact, you are paying to have emailable contacts in your Klaviyo account. So why would you want to pay for bot emails, misspelled, or otherwise invalid addresses? Invest your resources in building a high-quality contact list who wants to hear from you by using double opt-in.