Great campaigns need a great list
Without verifying your email addresses, you are essentially sending messages to a list of unknown addresses. Spend a few cents verifying your emails which will help build the foundations of a successful email campaign.
Get more replies from your emails
Working on your subject lines and the message copy are super-critical help improve your response rates, but without verifying your list, you may never increase your responses - no matter how good your emailing writing skills are!
Protect your reputation
In short, if you continue to send emails that bounce (as they are not valid), over time, this will affect your reputation. Poor sending reputation can affect your ability to send an email to someones main inbox (i.e. promotions or Spam).