When I'm writing hundreds of lines of frame layout code, I have to explicitly write `let transientValue:CGFloat = ...` hundreds of times or else the compiler quits on me saying that it was unable to infer the required type before timing out. The error makes sense if you think about what the compiler is doing (solving a system of equations with all of the number like built in types) but frankly it's unnecessary to begin with.
Compiler performance aside, it also makes working on code a lot heavier since the editor needs to be able to infer the types (something the full blown compiler struggles to do given all cores and tens of seconds!) before it can give sane autocomplete suggestions. I'm not sure if a better IDE than Xcode could handle this better but I've found the tools have forced me to be explicit just so I can get my work down more quickly.