Jeffrey explained in his blog post, that the PowerShell team had a problem in Windows PowerShell v1, that caused the binaries not to be NGENed.
What's NGEN? Managed code exists in Common Intermediate Language (CIL). The Just In Time (JIT) compiler takes that and converts it into native code for a particular processor/platform - a process also referred to as "jitter". If you don't want this translation to happen at runtime, you can use NGEN.exe - the Native Image Generator - to convert managed code from the CIL to native code. Native code does not need to be compiled at run time, and thereby avoids jitter.
So how does speeding up PowerShell help Exchange? The Shell is built on Windows PowerShell technology, and under the hood, the Exchange Management Console also executes PowerShell cmdlets. If you're running Exchange Server 2007 on Windows Server 2003, you're likely to see performance gains in shell start-up times after running this script. On one of my Exchange 2007 servers, EMS now starts up in as little as 2-3 seconds.
Read: Speed up PowerShell