I wonder why would a C++, C#, Java developer want to learn a dynamic language?
Assuming the company won't switch its main development language from C++/C#/Java to a dynamic one what use is there for a dynamic language?
What helper tasks can be done by the dynamic languages faster or better after only a few days of learning than with the static language that you have been using for several years?
Update
After seeing the first few responses it is clear that there are two issues.
My main interest would be something that is justifiable to the employer as an expense.
That is, I am looking for justifications for the employer to finance the learning of a dynamic language. Aside from the obvious that the employee will have broader view, the
employers are usually looking for some "real" benefit.
Knowing grep and ruby made it possible to narrow down a problem, and verify the fix for, an issue involving tons of java exceptions on some production servers. Because I threw the solution together in ruby, it was done (designed, implemented, tested, run, bug-fixed, re-run, enhanced, results analyzed) in an afternoon instead of a couple of days. I could have solved the same problem using an all-java solution or a C# solution, but it most likely would have taken me longer.
Having dynamic language expertise also sometimes leads you to simpler solutions in less dynamic languages. In ruby, perl or python, you just intuitively reach for associative arrays (hashes, dictionaries, whatever word you want to use) for the smallest things, where you might be tempted to create a complex class hierarchy in a statically typed language when the problem doesn't necessarily demand it.
Plus you can plug in most scripting languages into most runtimes. So it doesn't have to be either/or.
Why learn Perl, Python, Ruby if the company is using C++, C# or Java as the application language?