With an explicit error you get from validation (like Zod, as used in tRPC), you could notice that your client is out of date and either refresh automatically or

With an explicit error you get from validation (like Zod, as used in tRPC), you could notice that your client is out of date and either refresh automatically or prompt the user to refresh[1]. The benefit from validation is that the error is easily recognizable & can be handled nicely, even in just one place. Without validation, you get things that Typescript claims are impossible, for example exceptions on code paths that look like they cannot throw, and you can't easily tell why any of that happened -- that's a recipe for miserable debugging. Of course, with less busy, less critical, sites you might not notice or care. [1]: Refresh could cause loss of user input (e.g. text just entered), depending on the app that might matter and need browser-side storage or something along the lines of the "local first" manifesto. Easy kludge for simple apps with smart users is to make the user copy the text, click refresh, paste.