I've seen a couple of searches for this question. I looked it up myself and didn't find much information on it at all. I will explain! But first, remember we are talking about the actual service ONLY. IMA is also your local cached data store.
Independent Management Architecture Service (or IMA) provides the communication between servers in your Citrix environment.
IMA exists to manage your XenApp farm by providing a method of communication directly with each server. The types of data that are used through this service would be sessions, server load, licenses, and other data that you can view in your management tools. This communication exists on TCP port 2512 by default.
IMA is important for communication to your Citrix Application server but not necessary for current connected sessions. You can successfully stop IMA if needed to do things like recreate local host cache without effecting users that are logged in.