Problem: During development of an ASP.NET application, every time I recompile a specific assembly, it causes the entire site to get recompiled then IIS is taking more time to recompile pages again. It is time consuming, and causes frustration during debugging and fine tuning of elements in specific ASP.NET pages.

Solution: Set optimizeCompilations to false in web.config in compilation tag under system.web

This article from Microsoft MSDN describes the issue in more details