An essential part of marketing is redesigning a website, whether it's your client's or your own. It is important because trends, expectations and technology of clients change over time, and if we want to stay competitive in the market, we must keep pace with these things.
This task is important but also risky from an SEO perspective. Many things can go wrong during this task. In certain cases, some mistakes can also result in penalties.
During redesigning the website, many web designers' removes or rename the webpages and consider the task complete. But this is the biggest mistake because certain of those webpages may already rank well in Search Engine Result Page. Those pages might have inbound links driving to them or have been bookmarked by users.
When you do this type of mistakes, you will lose all your SEO value coming from those links, this could result in a huge loss of ranking in SERP.
This mistakes will also create a negative user experience when anyone clicking on those links will be resulted by a 404 error page. This is the most important factor because Google has confirmed that user experience is a ranking factor.
The best way to delete or rename any webpage is to redirect it to the most relevant page. A 301 redirect should commonly be used.
As soon as you redesigned a website, you need to review some pages to make sure all the things look ok and also functions properly.
None of these mistakes is particularly complicated or difficult to avoid. You simply need to be aware of them, implement a plan to avoid them, and pay close attention to detail.