The only tradeoff is not rendering speed, you're also required to use javascript, create an api to serve data(depending on the site this may be overkill), ship

The only tradeoff is not rendering speed, you're also required to use javascript, create an api to serve data(depending on the site this may be overkill), ship huge gobs of framework code to users, work with an ever-changing and complex landscape of tools which mostly demand you convert all your code to use that framework, put up with the slower speed, and run js on the server side too for SEO. There are very few upsides if you already serve pages server side and look at current client side js development.