Not much faster for me

Not a bug, just a comment / datapoint: In my project (2186 files) the new tsc incremental build option is faster than turning off type checking.

tsc-transpile-only builds in about 18s:
~~~~
$ time tsc-transpile-only -p build.dev/typescript/tsconfig-app.json

real 0m17.829s
user 0m32.632s
sys 0m0.792s
~~~~

tsc cold build is 21s, incremental is 12s:
~~~~
$ time tsc -p build.dev/typescript/tsconfig-app.json

real 0m20.863s
user 0m38.351s
sys 0m0.834s
$ time tsc -p build.dev/typescript/tsconfig-app.json

real 0m11.591s
user 0m22.628s
sys 0m0.507s
~~~~

The quest for faster incremental builds continues ;-)