With tRPC, changing an attribute of a class in your backend immediately tells you what broke in the frontend in your IDE. No need to recompile or regenerate anything.
Also, when developing your frontend, you'll have immediate autocomplete. Again without code generation or compilation.
That alone should save you dev time and prevent a ton of frontend bugs.
It slows down the iteration cycle - when you make a change to your API definitions you'd need to push the change to either a schema repository or into production, then regenerate the API - at which point, if you've accidentally introduced a breaking change, your frontend is already broken - you can work around this with CI that detects breaking changes, but it requires a fair amount of work. Having them in a monorepo means that breaking API changes can fail CI and never make it into production.
