SPA is very broad. Static content work best when delivering only the minimal assets needed to render. Googles AMP does a very good job at this.
Dynamic apps have a very different set of concerns. All SPAs aren't the same. Only the stateless, pure renders, like React and Vue, offer a compelling potential to unify the concerns of static content and apps that need to run across multiple platforms and network conditions. It comes at increased complexity and cost to maintain a multi-platform structure. If there's no business or consumer benefit there's not need to over engineer a solution to use a SPA.
Why is much more important than what to do. The best benefits of code reviews are:
1. Developer educate each other about the code base and how to be better developers. This means quick, more stable features which means the company can start making money sooner.
2. Slows tech debit. Poorly written code stays out of the product. More up time means more overt unity to make money.