This is one of the key questions for millions of Mac users who are about to receive the new version on their computers. There is no doubt that this is an important decision for many and it is that although nowadays the versions of macOS do not vary so much (at least between Catalina and Monterey) Yes, we can have some remnants of applications, tools or similar that can make a dent in the operation of our Mac.
Personally, in each of the new versions I perform a clean or zero installation on my computers. My iMac is old and no longer supports the new macOS Monterey but certainly in my case with so many tests that I do on it it would be a safe clean installation.
Has it been a long time since you updated your equipment from scratch?
This is the key question in these situations since although it is true that Apple does not recommend installing from scratch at this point, it is sometimes the best when We have not put a clean version on our Mac for several years. In any case, the decision is always in the hands of the user, so there is no problem in any case.
The habits of users, especially the most veteran Mac users, is another issue. Today and seeing Apple’s OS optimization it is no longer so important to do this installation from scratch but it is possible that you have that habit every time a new OS arrives and therefore the answer in that case is that you continue with it since it is not so difficult to do the clean installation and less when we have it at hand.
On the other hand, there are users who do not have failures in tools, applications or the system itself takes more and more time to open and therefore an installation on the current system is not going to hurt them and possibly the functioning of the Mac will improve. As I said at the beginning It will depend on many factors, but nowadays it is no longer an obligation to perform a clean installation when a new version of the system arrives. What is important in these cases is that before launching to update or install from scratch you make a backup copy on your Time Machine.