First: IronPython is really more of a compiler than an interpreter in the strictest sense - it will be used to generate .NET Assemblies from your python source files. So yes, you can write apps and most anything the .NET Framework can do.
One of the largest benefits of IronPython is that it has (effectively) no GIL - meaning that if you are both writing Python code and it is multi-threaded - you can often get performance that is better than CPython without having to spawn multiple process and pickle objects across the boundaries. It doesn't solve the problem of concurrency, but .NET provides much more robust constructs for dealing with it. I think this is pretty niche honestly, but it is certainly there.
The python.org wiki page for IronPython lists a bunch of key differentiators as well:
