But bear in mind that Python on a server is likely to run much more quickly than it would in a browser because the server is likely to be a much bigger beast.
For me the advantage is that you don’t have to worry about server side frameworks and deployment is as simple as any other web page.
The disadvantage is that on weak hardware a PyScript app takes quite a long time to get going (2 minutes on an old Windows tablet). So, from the user point of view, a server based app might be better.
Also, PyScript is very much in the alpha stage so it would not be a great idea to build anything serious with it at the moment.