Changing to a new domain name should be avoided in the first place, but there could be situations which could compel you to migrate to a new domain name. This could be a cause of concern as you may experience your traffic nosedive. However, if done properly your website could be ranking on top of the search engine again in no time.
Reasons to change to a new domain could be many. The most common ones being, selecting a lousy domain name in the first place, change in name or focus of the business, a better-suited domain name which was previously unavailable being ready to be used now, or something that damaged the reputation of the domain.