Can anyone explain what advantages there are to using a tool like MSBuild (or NAnt) to build a collection of projects versus running DevEnv.exe from the command-line?
<The prime reason for using an external build tool like NAnt or MsBuild is the ability to automate your build process and thus provide continous feedback on the status of your system. Also they can be used for loads of things besides a "pure" build and that's where you really start to get value from them, it's an extremly valuable thing to be able to build and test your application with a single command.
You can also start adding stuff like collection of metrics, packinging of release binaries and all sorts of nifty stuff like that.
The obvious answer from my team is that not everbody has visual studio installed, in particular we do not install Visual Studio onto our build/CI servers.
We are experimenting with switching from DevEnv to a tool (Visual Build Pro) that uses MsBuild under the hood and we got a "Reference required to assembly 'System.Drawing..." error for a project which doesn't need it and which builds fine in Visual Studio.
One reason is because there's much more to building a product than just compiling it. Tasks such as creating installs, updating version numbers, creating escrows, distributing the final packages, etc. can be much easier because of what these tools (and their extensions) provide.
While you could do all this with regular scripts, using NAnt or MSBuild give you a solid framework for doing all this. There's a lot of community support for both, including additional tasks that can be downloaded (such as the MSBuild Community Tasks Project). Plus, there's support for them in numerous third party and open source products.
If you're just interested in compiling (and not the entire build process), you may find one time saving benefit of MSBuild is the support for building with multiple processors.
We have a large system consisting of C#, managed C++, and plain old unmanaged C++ assemblies/dlls. There is C++ code that depends on managed C++ code that depends of C# code that depends of managed C++ code that depends on plain old C++ code (whew!). When we were setting up our automated build environment a few years ago we discovered that MSBuild.exe didn't properly handle all of the dependencies that we have.
Working with Microsoft we were able to solve some of the issues but not all of them. If my memory serves me, we never could get the C# assemblies that depended on managed C++ dlls to build. So we ended up making a custom build script that called devenv.exe from the command line and it worked just fine.
Of course, that was with VS2005, it might be fixed now, but the script is still working so we haven't revisited the issue.
As far as C# goes, devenv.exe 2005 runs the compiler in-proc, which may cause out of memory exceptions for sizable solutions. Msbuild resorts to launching csc.exe process for each project. Projects that don't compile with devenv /build work fine with msbuild. Hope you like this reason.