People often ask what the aspnet_compiler tool can do. The usual answer is "pre-compile an ASP.NET 2.0 web site". The follow up question is: "What good does that do me?". MSDN says the advantages to compilation in general are:
Let's take these one at a time.
I say the performance benefits to pre-compiling a site are negligible. Pre-compilation does save some work, but ASP.NET applications in general are slow starters. Think about all the work that happens when the first request arrives. A process has to start. An AppDomain has to load. The cache is empty. The database connection pool is empty. Even if you've precompiled, the JIT compiler has to step in and create native code.
I'm not saying you shouldn't pre-compile a site to save some time. Just don’t' count on seeing a significant reduction in start up time for all applications.
The MSDN article I linked to says "Compiled code is more difficult to reverse engineer than non-compiled source code…". Compilation makes the job more difficult, but all someone needs is the right tools. If you are trying to hide secrets in your source code, then encryption, not compilation, is the way to go. If you want to protect intellectual property then look for good obfuscation tools. Just remember you can't stop reverse engineering, you can only slow it down.
I don't think of pre-compilation as a security benefit, but if you pre-compile an ASP.NET application without the updateable option, you will lock down the application in production. Pre-compilation can strip out all the markup in template files, and no one can easily hand-tweak stuff outside of the configuration management process.
I never thought of interoperability as a benefit of compilation, per se. It seems interoperability between languages is a feature of the platform, not any compiler. I think the documentation is stretching this a bit.
ScottGu refers to using pre-compilation for "deep verification". A pre-compiled ASP.NET application is stable and verified in the sense that you won't see runtime errors because of syntax problems in markup. If someone checks in a malformed server control tag, you can catch the problem during the build with a compiler error, instead of finding out about the problem in test or production. Stability is arguably the greatest benefit of pre-compilation, and I recommend pre-compiling a web site for this reason alone. .
When I heard about pre-compilation in ASP.NET 2.0, my thoughts circled around startup performance. As it turns out, pre-compilation will save not only CPU cycles but test and development cycles as well. Pre-compilation is worth the effort, primarily because it requires so little work to setup.
If you want an interactive and user friendly interface for pre-compilation, check out Rick Strahl's ASP.NET 2.0 Compiler Utility.
Web Deployment Projects can do pre-compilation (and a whole lot more), using a standard MSBuild project file.