I'm working on a site that was created a few years ago and already has GA. It also has GTM for some other tags. I want to understand is there a good reason to update the already working code and move GA inside GTM? Also, can this somehow improve or break site performance?

P. M. I understand that GTM is more flexible and you can change your tags without touching the main code. But in my case, GA is already implemented outside GTM and I need a good reason to do this change))

Thank you!