Visual Studio loves file I/O. It really, really does, and it cares very little about caching and the like. What this means is that, when you open a solution file, it always reads it from disk. Which means that the speed of operation when generating lots of files (e.g., via T4 transformations) is typically atrocious. The fact that file I/O in VS does not appear to be multithreaded is another hindrance. In short, it’s a mess.