"Execute business operations in CIL" or not?

In AX 2012, steps are taken by the development team at Microsoft to align AX IDE with .NET. That's why you regenerate the CIL after X++ code changes.

CIL obviously has its benefits like faster execution in cases of heavy logic processing.

But sometimes while testing or debugging, developers would prefer NOT to avail this option. Debugging can be cumbersome in AX 2012 as you will need to configure Visual Studio for code running in CIL. The solution is to uncheck a checkbox in Options at
Tools > Options > Development > General > Execute business operations in CIL

Now even the code which was running in CIL will now run in X++ interpreted mode, the old way.

Word of caution, this option should only be used by developers while debugging. It should ideally be checked again after work is finished.

Read more at http://msdn.microsoft.com/en-us/library/hh528509.aspx