Speed and Responsiveness: Since most resources (HTML/CSS/Scripts) are only loaded once, and only data is transmitted back and forth, SPAs can be significantly faster and more responsive than traditional web applications.
Simplified and Streamlined Development: SPAs can be easier to develop because you don't need to write code to render pages on the server. You can use the same backend code to generate data for both your web application and your API.
Improved User Experience: With no page reloads and fast transitions, SPAs can provide a superior user experience that's similar to a desktop or mobile app.
SEO: Historically, SPAs have had a difficult time with search engine optimization (SEO) because not all search engines execute JavaScript during crawling, and thus, may not index all the content.
Initial Load Time: SPAs can have a slower first-page load time since the entire application needs to be loaded upfront.
Browser History: Managing browser history can be difficult in a SPA. Because pages don't reload, the browser's back button may not work as expected without extra work.