Let's start out with a question - What is a website migration?
During a website migration, a website undergoes changes to its structure, URLs, content, design, and sometimes even the platform that it's running on. Website migration can be as simple as changing the URL structure to be more user friendly, or moving completely over to a new content management system (CMS).
There are many different types of migrations that exist, but the key factor in the equation for all of those migrations is ensuring a smooth transition, and avoiding any types of performance drops such as losing your hard-earned Google rankings.
Whenever you migrate websites, you want to ensure that you do it the correct way. The correct way is by mitigating any chances of traffic drops due to an incorrect migration. In some cases, it's possible to remedy traffic drops and rankings losses, but a much easier way is to avoid them altogether in the first place.