Increase your credibility
Buying an email list may do other things but it will never increase your projects credibility. Your emails will only end up in spam/trash folders. A self-respecting dev would never buy this serives.
Well i respect your opinion buddy. That why they are called email campaigns out of 100,000 emails you may end up converting some percentage. We have used such lists countless times with immense sucess in launching ICOs and Cryptocurrency blogs