With the days of small games and applications generating enough revenue to make a living from them being gone, even in the mobile space, its unavoidable that our projects grow in size and often also in code complexity.
But unfavorably for us, Unity is not exactly helpful when it comes to maintaining code quality and ensuring that regression is prevented.
This is caused by different aspects, but the largest ones are that the debugger tends to have some more or less ugly problems, by Unity Technologies refusal to finally provide mdb files to include their own closed source in proper debugging and by the lack of proper unit testing support.