I have written a couple of thousand lines in an app the last year and I have already had problems with restructuring my app. Creating new modules and moving "classes" into them or splitting classes and renaming them are very useful things and those things get easier with types. Having tests actually don't help that much with this in my opinion since I have to rewrite the tests also. Also reading old code could get easier with some type information in the code. Just my experience so far.