I like that it lets me send mass emails with one click, which saves time for every person involved in managing my business's email campaigns! It also has an easy to use editor so you can easily create beautiful newsletters without needing any design skills or coding experience at all (which is great if your team doesn't have those!).
The only downside of this software would be its price tag ($10/month). If their pricing model changed then maybe people wouldn’t think twice about paying $1 per month instead of 10 times more than they do now? We used MailChimp before but found out we had no control over our subscribers' inboxes whatsoever - not even when somebody unsubscribed from us accidentally via spam filter etc., unless someone manually checked each mailbox individually after receiving these messages.