Migrating business critical applications to the cloud is not a project which can be done on a whim without serious strategic thought. Application performance management tools offer an insurance policy of sorts, they give you the visibility into performance before and after migration. Having a true understanding of application performance, a baseline if you will, is the only way to suceed with migrations:
What are the methods available to move to the cloud? How do they stack up to what actually happens. Theory is all well and good, and I have read plenty of those architectures, but when the shoe leather hits the cloud where are we? Here is a short history, a comparison of methods, and some conclusions that can be drawn from our migration to the cloud.
You can read more here: Migrating Business Critical Applications to the Cloud